I think fighters are really down to execution.
If you look at the last Mortal Kombat reboot, they did not add a whole lot of new stuff (save the X-ray mechanic, which I'll discuss shortly).
The game was all about interesting key combinations that really felt organic with the outcome (combat move) and sufficient feedback and a overall sense of fairness (balance).
1. Just it being done right, playtested and re-balanced (probably a bunch of iterations) and have a lot of feedback so I'm not left wandering if my move hit or miss.
2. X-ray. It's not that I hate it, mind you. I understand the idea of capitalizing on an opponent's vulnerability by using a "risky move" that depletes some form of limited resource, but I believe the implementation was sluggish and more about wow-factor. I would've preferred either having a standard move that leaves me vulnerable if I miss or hit a block I'm guessing.
3. RPG elements? Not sure how that could work. I know an earlier Mortal Kombat tried that and failed miserably. I'd like to level up my fighters to unlock all of their special abilities. I also like the idea of weapons, and very few fighters actually use them (though the new Mortal Kombat will!)