natural pathway of things : Injustice is the hype stuff right now, while MK9 follows its own track, third time in a row in Evo
when Injustice come out, majority of MK players will try it, to see if it's indeed a good game with competitive feeling
I doubt MK9 will be in Evo in 2014 (could be wrong, but ...) and until there, Injustice will have time to grow its own community, and great part of it, has chance to be from here, TYM.
MK10 , sure will be made and released something in the next 2-3 or 4 years ahead, and NRS will bring all previous experience built in MK9 and Injustice, to make a MK game even better than its predecessor
I see MK9 being replaced naturally, by Injustice and a new MK game, according the natural time cycle ..... it still will make part of some majors, but, overall, others game will take the spotlight, sooner or later.