I really want to see them return MK to its roots. Maybe not completely since the roots are pretty basic by today's standards, but it seems like Boon wants to at least make it more like old school FF again, making fatalities the center focus. Fatalities and gore in general are both tame and pretty much expected by today's standards, but if they came up with a fresh interesting way to implement them or just flesh them out a lot more than any other game has (extreme internal organ detail, etc). Make them SHOCKING. Make them controversy-material, like Manhunt 2's.
Push the limits of what the console devs would allow on the system, and if it gets you an AO rating.......good. As long as it's not rated AO for sex, I can see MK9 actually being a video game industry milestone as the first AO game to be officially released on at least two consoles. After that, AO ratings would start relaxing, and we'd start seeing some really crazy stuff, and then video games would finally be on par with movies, as the rating system should have been in the first place.