In the latest episode of Gametrailers TV, Geoff Keighley talks with Mortal Kombat creator Ed Boon about MK9. In the interview we find out that Jax and his infamous subway level are going to be making a return. On top of that he also mentions that there will be downloadable characters after the game launches but the final roster or price of the DLC have been finalized.
If you want to hear the information first hand you'll need to watch the episode.
I know its old but thought it was interesting.