MK10 in 2015
Injustice 2 in 2017
It's takes them 2 years to make a game, and they will alternate to avoid causing burn out on either franchise. They have talked about this a million times already in interviews leading up to Injustice.
The only thing that might throw a wrench in the loop is if they make a non fighting game, which Boon has talked a lot about wanting to do, especially a MK SM2.
The only chance we might see anymore Injustice content before 2017 is either some random pity DLC, or some kind of Injustice 1.5 with a few new characters and balance tweaks, as a way to keep the competitive scene alive so it doesn't die as soon as MK10 comes out, like what happened with MK9. However, I really doubt they would waste time and resources on that.