You can see the "rules" of these posts here.
Must-Have Minifigures (A): Cyclops, The Beast, Jean Grey, Gambit, and the one and only Wolverine. We've almost had 50 years of mutants to potentially draw on. Imagine a minifigure Juggernaut or Magneto! Jamie Madrox alone would be an instant battle pack (the real fans know what I'm talking about)...
Propensity for Vehicles (C): I could see a UCS Blackbird or a motorcycle for Wolverine, but not much beyond that. Minifigures and playsets like The Danger Room are more likely to drive this line.
Preexisting Fan-Base (A): 50 years of comics, cartoons, and live-action movies. Nuff said.
Depth of Theme (A): You have Charles Xavier's first students, you have X-Force, X-Caliber, New Mutants. Age of the Apocalypse. If the line gets stale, you can have Grant Morrison come in and reboot the whole series with a psychedelic slant!
Kid Friendliness (A): Kids used to love the movies and cartoons, but its been awhile since I've seen Wolverine on a t-shirt adorning anyone under the age of 12. Although I haven't seen the show myself, the kids seem to like The Super Hero Squad Show on Cartoon Network. If you took it in that direction it might be more appealing.
Likelihood of License (B): Last year Disney bought Marvel to up their 'boy-cred', which is desperately needed in its endless kingdoms of fairies and princesses. This seems like it could be a good fit if the Toy Story and Prince of Persia sets are seen as financial successes.
Overall (B+): If done right, this could hit a sweet spot with both AFOLs and kids, but a balance must be struck. Too mature and parents may shy away. Too cutesy and the AFOLs will pass it by. The 'superhero' lines of the past have been a mixed bag. LEGO Batman was not financially successful until after the sets left the shelves and the video game took off. I don't know how successful the Spider-Man line turned out to be before Mega Bloks got the license in 2004. In the end a lack of vehicles may be the downfall of this idea.
Custom Options: Whenever there's a vacuum in the AFOL community, some creative individuals find ways to fill it.
Kubrick had a line of X-Men figures they sold back in 2004. Although still different from a minifigure form, it gives you a sense of what these could look like. This would be an interesting way to add a 'maxifig' scale with Sentinels.
There have also been countless custom minifigures built with the mutant gene. Fine Clonier has decals for key X-Men. BrickForge has their Savage Mask. I've seen some cool claws for Wolverine, but I've heard they are from the Mega Bloks line (Ack! Competitors!). The new claws from the Prince of Persia line just don't cut it.
It would seem that Magneto is threatening mankind once again. Away to me my X-Men! We still need to build the Blackbird before we can save the day...