I'm thinking some stage fatalities will show up for sure. I was downright surprised there were only 6 of them. The 6 are really good, I think, but so many of the stages have obvious ones they didn't include. I mean, you don't need a creative mind to realize the Pit Bottom could easily have a friggin fatality. I'll bet they had many ideas drawn up and are just going to trickle them in with other new content to keep the game fresh.
I voted Friendships. Those would be great, especially if there were rules to doing them (I'm not clear on Babalities, I've read "don't block" but I've never had trouble performing one).
Of course I want more regular Fatalities, it seems like the engine can easily support and create new ones. Especially with the way they have bodies flying apart already created.
Classic fatalities I would love. Not just the existing retro 3, but for all characters. Would be a great nostalgic throwback.
Animalities sucked IMO. But I think a lot of that had to do with the graphic style they incorporated in MK3. They'd be cool to see now that the tech is better, but I doubt we'd get those. Way too much programming -- maybe MK10.
Hara Kiri's were kinda cool, though they didn't make a ton of sense, the fact the dead player could do something was interesting.
Brutalities will be in a future update, I'd bet my koins on it. That would be ridiculously easy to program in. Again, I think that's a matter of them intentionally not putting all the content/ideas in to keep the game fresh later. Kind of how each arcade board revision added new stuff.