Ed Boon updated his Twitter account with a Roman numeral "II" logo and responded to a fan question of, "Why is this for ? MK 11 OR INJUSTICE 2?" with "That is a DAMN good question...."
We're guessing it's for both.
Rumor of the Injustice: Gods Among Us video game sequel hit a few days ago with mention it may be announced at or around the upcoming E3.
It's also probably safe to say that more than likely, another Mortal Kombat game is in development, with Mortal Kombat X having been so well received.
The E3 takes place June 14-16, so look for announcements soon.