It might be worth mentioning that Mortal Kombat X's first DLC trailer (which revealed Tanya, Tremor, Jason, and Predator) was released exactly three weeks before the game came out. We're approaching the three week mark for Injustice 2, so maybe we'll get a DLC trailer in the next few days.
A DLC tease at the end of the character reveal trailer on Friday would be pretty sweet.