What if Injustice 2 was Marvel vs DC? Lego Marvel Super Heroes means that WB Games and Disney/Marvel have already collaborated, and that started development before Injustice 2 did, which means that the potential is there for them to have a working relationship that lets this happen. Marvel mentioned that we'd start hearing about console games with big developers sometime this year. Plus Injustice was about the DC heroes stumbling into an alternate universe anyway, imagine if the second one was them going to the Marvel universe.
Do I think it's likely? Nah, I don't think I could confidently make that bet. But it maybe, just maybe, could happen, and I wasn't able to say that 2 years ago.
Anyway whatever NRS' next game is, it's probably a March/April 2017 release. A new fighting game in one of those months, every two years, is the pattern they've been following since MK9.