With the launch of Vs. System 2PCG a lot of people have been speculating about which properties will be included in the base set. In the 2PCG Changes & Rules Primer
we have already been told who some of the Main Characters are: Captain America
... so that clearly points to Avengers and all the storylines that point to Thanos
and the Infinity Gauntlet
(ie. Guardians of the Galaxy
What you might not realized is that there's something else going on in the Marvel Universe that greatly impacts what characters are available to licencors ... a character's movie rights.