I think they should do a few things. A. for nostalgic, oldschool reasons like MK 9 brought back. Have the fatality time a little bit shorter, instead of 5 seconds or so make it 3 or 4. Second, make it so that you can only move back and forward(pretty much to get rid of people who want to teabag waste time) , with the ability to hold block(as some fatalities required that in past MK's) while say a command is "^ ^ > ^+B" something like that for sure, I think those would be cool updates for Fatality time!
I'm also for more grittier, nastier, darker fatalities(I know they've pushed the envelope too far already at times lol) but always love a brutal fatality and give everyone at least 3 fatalities each this time, maybe 4. Besides of course stage fatalities, example that MK 4 fan stage MUST return!! hehe