NetherRealm has a little fun with Mortal Kombat fans' predilection of wild goose chases and suppositions.
A bit ago NetherRealm senior production manager Jonathan Andersen reportedly posted up a Mortal Kombat image on Twitter...and then promptly deleted it. At first glance everything looks normal--it's just some old legacy artwork for Injustice and some Mortal Kombat adverts. Closer inspection (look on the upper right) reveals some interestingly-named desktop icons: KI_Planning, dinosaur, and a reference to MK12.
Even closer inspection reveals a tongue-in-cheek email from Christine Letheby, NetherRealm's production manager, which mentions: "Our fans eagerly scrape the internet for any trace..."which is undoubtedly a nod to Injustice 3 and Mortal Kombat 12 theories floating around.
While this exchange might be a good-nature goof, there's evidence that NetherRealm is indeed working on Mortal Kombat 12 instead of Injustice 3.
Our own investigations on NR job listings seem to indicate this, and VentureBeat's Jeff Grubb also says MK12 is next on the docket.
The studio is currently hiring for a number of positions but none of the job listings give away much info. We can glean that NetherRealm will continue making (or at least maintaining) new mobile games, and that Mortal Kombat 12 will indeed have a live service offering built around NetherRealm's internal KoreTech infrastructure.