MAGNETO
While I think a Brotherhood of Evil Mutants comic could be really cool and a lot of fun to read from their perspective, the solo effort fits best. Now this comic could easily go one of two ways, or both ways if they planned it right. Moving along currently in the present showing Magneto descending back to his wicked ways or you could go to the past and show influence from the X-Men: First Class film and show Magneto hunting down Nazis (an idea I’d be fond of seeing). Of course you could do both, showcasing Magneto’s current evil plans and how those mirror or relate to things he did in his past.
Likelihood of happening: I’m not holding my breath on this one but I would really really like to see it (in case you’re reading Marvel).