I buy these entirely for the story mode, so as long as they knock that out of the park again, I'm good. I was really looking forward to whatever story they'd do with Injustice 3, but trying other franchises is exciting, too. Gives them more time before going back to MK proper, too.
Also, MvC is slick, but neigh unapproachable for casual fans. The ceiling is just too high and, out of every fighting game I've got (most of them), the neatherrealm games always got the most play with random non-fighting game friends b/c, even if button mashing feels stiff, you can still do enough cool stuff for it to look cool.