I really enjoy the Fatal Blow mechanic in MK11, I think that it is a really clever idea that I would love to see cross to Injustice in some form, is that something that people want to see?
From my own point of view I have two ideas to make them distinct from MK11
1: Fatal Blow type mechanics are a condition for Stage Transitions (or unique Stage Transitions)
2: Fatal Blow type mechanics that are used defensively (eg Block a projectile 3 time you get an auto counter or gauge refill etc?)