No X-Men sure. No Street Fighter not really. Marvel has MUCH more to offer then X-Men. Capcom fighting game wise is mostly Street Fighter. Making a fighting game without it is doable, but kinda crippling.
No street fighter characters would cripple them, but it looks like this time they're going a bit to far in the other direction. I can live with no X-Men, but so far from the Capcom side of things all we've seen are SF and Mega Man, and if the rumors are true and those are the only two franchises we see I'm gonna be pissed. Like I don't need a stupid big MvC2 roster, but there are just so many games to draw from, and it would be stupid to leave someone like Strider who's been there from the beginning out.
Also, what do people think is going on with the infinity stones? My guess is it's a more customizable but otherwise pretty unchanged X-Factor, but I could also see it being a revenge gauge type deal a-la v-trigger and ultimates.