In a team book or as a supporting character, you only need to help advance the story, playing a small role in an overall team dynamic. However, a lead character needs compelling personal motivation and a personality well-rounded enough to keep readers coming back for more. It also doesn't hurt to have a place to call home, some friends, and a personal life. These are important details that are either missing or poorly developed when most supporting superheroes begin their own ongoing series.
To survive competitively as an ongoing title, these women will need to create the proper context to showcase the most compelling aspects of their character. It isn't easy to do. Regardless of gender, creating the proper context for your characters is a sublime art that sometimes takes years to develop, and that's time you don't have in the modern marketplace.
However, I think Marvel can create successful ongoing female lead titles if they just find the right character and build the proper context for them. Below are some of my recommendations:
Potential: Highly recognizable, great costume, military background, diverse connections throughout the Marvel universe
Problems: Lacking strong motivation, generic power set, history of victimization and dependency
Enemies & Allies: Kree, Mystique, Rogue, Mar-Vell, Wolverine, Starjammers, Avengers
Recommendations: Avengers: Earth's Mightiest Heroes cast Carol Danvers as both superhero and agent of SWORD, similar to Captain America's arrangement with SHIELD. I think that makes sense with both her powers and background. Also, placing her in the role of Earth's first line of defense against alien threats to Earth gives her a unique place in the Marvel universe. Working with SWORD would give her an interesting supporting cast that could consist of aliens (like Mantis) or other unusual creatures (Vision), offering the advantages of both a team book and a solo series. I would build up to a conflict with a Kree to connect to Carol's origins and explore their culture in more detail. Although Carol has a history of victimization and dependency caused mostly by poorly executed stories, this could be a source of strength in the story if you are willing to explore her self-destructive nature and fears of inadequacy or abandonment.
Potential: Strong motivation and origin story, espionage
Problems: Un-spider-like powers, no actual connection to Spider-Man is confusing, bad costume
Enemies & Allies: HYDRA, SHIELD, Lindsay McCabe
Recommendations: Experimented on by her father and given to HYDRA as a superhuman spy, Jessica Drew works best with her back against the wall. Created by deceit and manipulation, she should live in the shadowy, fugitive world of superhuman espionage. Contacted by SHIELD to act as a freelance, unofficial agent, she works with minimal support to investigate superhuman experimentation and terrorist organizations, sent to investigate superhuman threats before they can become Avengers level catastrophes. However, the deeper she gets into her work, the more she suspects that she might not be working for SHIELD at all.
Potential: Highly recognizable and respected, interesting powers, African, thief, claustrophobic
Problems: Lacking strong motivation, has little identity outside of the X-Men
Enemies & Allies: Shadow King, Forge, Yukio, Black Panther, Morlocks, Adversary, X-Men
Recommendations: Ororo has a lot to draw on through the death of her parents, her days as a thief, being worshipped as a goddess, joining the X-Men, claiming leadership of the Morlocks before their slaughter, and marrying the Black Panther. Unfortunately, her nobility and lack of relateability are impediments to supporting her own title. I would team her up with Yukio, the free spirited Japanese thief who ignited Storm's original mohawk phase. For her arch villain, it only makes sense to use the Shadow King, the first villain in her life who essentially enslaved her. He could attack her where she is most sensitive, through Forge, Black Panther, and the Morlocks, drawing Storm through some of her most painful memories while simultaneously informing the reader to her backstory (while avoiding the context of the X-Men). Considering how adrift the character has been and the bad decisions she has made (namely marrying Black Panther), it would make sense if she lost her confidence and needed time away from the X-Men and the Shadow King took advantage of this moment to get back at her. I would also relocate Storm to the X-Men's briefly used Australian base to call back to her original mohawk days, include the mutant teleporter Gateway as a spiritual guide, and just to evoke that Mad Max Beyond Thunderdome iconography. Maybe Storm could even become an Australian national hero.
Potential: Interesting power, highly popular, dark and mysterious past
Problems: Power is no longer out of control, phonetically reading her accent can become tedious
Enemies & Allies: Mystique, Gambit, Brotherhood of Mutants, Magneto, X-Men
Recommendations: Rogue has long been a victim of circumstance who has learned to redeem herself through the X-Men, even leading her own team on several occasions. We know that she was raised by Mystique and Destiny, and that her power first manifested when she kissed a boy, but we've been given very little insight into that experience. It would be interesting to know what it was really like for her growing up with two mommies who were also international terrorists training her to be the same. When she was first introduced, Rogue had no reservations about using her power, so it would be fun to see that Rogue... one who is constantly borrowing a piece of other people's individuality. I would like to see a story that brings Rogue into a confrontation with a victim of her terrorist activities, perhaps someone seeking revenge. This could convince Rogue to personally atone for some of the mistakes she has made and, at the same time, find a new direction in life. Just avoid bringing Gambit into the story; that sleezeball brings her down to a Twilight level of insipidness.
Potential: Ninja, highly popular, interesting power, diverse connections
Problems: Convoluted backstory, lacking distinct personality
Enemies & Allies: Kwannon, Spiral, Captain Britain, Slaymaster, Jaime Braddock, Archangel, X-Men, the Hand
Recommendations: With a backstory as complex as Psylocke's, I think the best approach is to embrace the absurdity as a motivating factor in the story. I was always a fan of the original version of Betsy, so I would bring back her bodyswapped Caucasian counterpart Kwannon (particularly because she was blind at the end and a blind psychic is a cool idea). It could be the work of her omnipotent and insane brother, Jaime. The unnerving part is that Kwannon (who insists on being called "Betsy") has revealed to Psylocke that their original minds are re-establishing themselves. Kwannon has forgotten most of her martial arts skills and Betsy is forgetting details of her childhood in England. The difference is that, due to Kwannon's tragic background, they would both rather be Betsy. [Naturally, this could get confusing fast, so you would have to resolve the name issues quickly. Maybe call them Betsy and Liz...]
Potential: Thief, great look, popular, strong backstory
Problems: Lacking strong motivation, frequently plummetting neckline
Enemies & Allies: Spider-Man, Kingpin
Recommendations: Thieves can be difficult characters to write in a superhero books because they are either anti-heroes or Robin Hood-type altruists. As a hero, Black Cat would be fairly generic, but if someone like the Kingpin were to blackmail Black Cat, she could return to the life of crime by stealing from SHIELD, the Fantastic Four, and the Avengers, thereby sinning in a manner that cannot be easily forgiven. The trick is finding the right McGuffin. Perhaps someone she loves is taken hostage or there is special information she can't get anywhere else. It should be something that drives her. If she is burning her bridges in the superhero community, she will be a fugitive, but that is just the threat. We also need a goal.
Potential: Great look, simple but compelling powers, great for heavy action
Problems: Lack of identity outside of X-Force and Cable
Enemies & Allies: Cable, X-Force, Copycat, Deadpool, Mutant Liberation Front
Recommendations: With luck powers, Domino seems like a good character to explore fate and freewill, particularly since her ex-boyfriend is a time traveler from the future. Perhaps Domino is told of a horrific fate that's destined to occur and with her luck powers, she is uniquely skilled to prevent it... even though she is told that is impossible. Since Peter David's X-Factor is almost over, if Layla Miller is still available, she could play the oracle who is trying to use Domino to avert the Days of the Future Past timeline. It might start off with some very practical attacks on anti-mutant hate groups and mutant terrorists, but Layla begins to ask Domino to do hurt innocent people without clear consequences based on what will happen in the future. Essentially, they are trying to knock down the dominos before fate can get there first.
Potential: Great look, strong iconography
Problems: Generic mythological entity
Enemies & Allies: Thor, Asgard, Defenders
Recommendations: Simply put, Valkyrie is Brunnhilde of the Ring of the Nibelung cast into the world of Thor. It would be fun to take the traditional silver age Thor backstory of being cast in mortal form and use it with Valkyrie. Without a mortal counterpart, Valkyrie doesn't have much to ground her, but if average woman Barbara Norris were to suddenly discover that she was a Valkyrie, drawn inexorably toward death, it could be a very interesting series. Although initially resisting the macabre pull of the dead, she comes to have sympathy for the deceased and takes pride in both comforting the dead and avenging those who deserve it. At the same time, the reason for her resurrection into the mortal world is a mystery to her and, though she is certain it is the work of the gods, she does not know if they are friend or foe.
Potential: Great costume, compelling backstory
Problems: Unrecognizable, powers are somewhat confusing
Enemies & Allies: Thunderbolts, Moonstone, Baron Zemo, Genis-Vell
Recommendations: Of all the reformed criminals of the Thunderbolts, Songbird has always been the one who showed the most potential of being a true hero and she seemed destined to become an Avengers. However, the story of the Thunderbolts has always been a tragic one and their downfall has repeatedly taken her down too. It would be interesting to see her at her lowest, confined to a superhuman prison ("Jailbird" or "Why The Caged Bird Sings") while Baron Zemo and Moonstone run free. Although initially she had intended to serve her time, she soon realizes that she has a life sentence and no one cares about her time as a hero... except the other inmates. Realizing that redemption can only come from within, Melissa decides to break out of prison and with the help of her old teammate, the Fixer, she sets out to bring Baron Zemo and Moonstone to justice.
Potential: Powerful magic user, tragic backstory, dark alternate personality, popular
Problems: Complicated backstory
Enemies & Allies: Belasco, Colossus, Storm, Kitty Pryde, N'Astirh, Madelyne Pryor, Darkchylde (herself)
Recommendations: Illyana has always struggled between her kind nature and the horrors she experienced in the demon realm of Limbo. Struggling to be the hero Magik, she has often succumbed to her dark side by transforming into her demonic counterpart, Darkchylde. Although she has tried to find a home with her brother in the X-Men, she keeps bringing the evil of Limbo back to her to threaten her friends and family. It would make sense for her to leave them all to learn how to control herself and overcome the pain of her childhood. Provided he is not otherwise engaged, I would have Illyana study at the foot of Doctor Stephen Strange. Not only is he the foremost expert in magic, but he is also a doctor and she is in desperate need of healing. He could guide her on a journey through the mystic realms that could considerably develop this side of the Marvel universe.
These characters didn't make it to the list because I honestly couldn't think of a solo series concept that they could support. Usually its an issue of poor motivation or lacking the right context for their character, but in the right hands and with the right concept, I believe these characters could all lead their own successful title:
Black Widow, Hellcat, Phoenix, Jewel, She-Hulk, Wasp, Elektra, Mystique, X-23, Shadowcat, Banshee, Echo, Emma Frost, Crystal, Tigra, Daughters of the Dragon, Firestar, Dazzler, Namora, Jubilee, Shanna the She-Devil, Rescue, White Tiger, Mockingbird, Mantis, Monica Rambeau, Scarlet Witch, Polaris, Sersi, Moonstar, Clea, Surge, Blink, Diamondback, Snowbird, Spitfire, Nomad, and even Squirrel Girl.