Not only is that a strictly Street Fighter thing, but it's a Street Fighter 4 thing. It's not like parrying or combo breakers where they are real life concepts adopted by many fighting games. It's an abstract video game concept used as a hallmark of only one franchise. X-Ray moves are already similar enough to Ultra Combos, and they ditched the pro-moves for Ex-style advanced attacks, but a lot of games have stuff like that. Focus attacks in MK wouldn't be completely out of place, but they would be a game mechanic lifted directly from SF4. The Mortal Kombat team has been doing a good enough job of not overly-mining Street Fighter for ideas (compared to other 2D franchises especially) it shouldn't start taking from them arbitrarily. Things like juggling attacks that freeze or pop up the opponent for extra hits are ideas started by MK. I think going in the direction of new ideas (even when they don't ALWAYS work) is the right way to go.