Danny D sent over a link containing a list of achievements for Mortal Kombat that reveal that Cyber Sub-Zero and Quan Chi will be unlockable characters. If they are playable or not is yet to be seen, but I wouldn't doubt it considering it looks like there will be no end to additional characters via DLC.
The same list also hints at a few other things, such as "Complete-ality" where it mentions you must perform one of each "-ality". Does that mean we can expect things like Anamalities and Babalities? Hmmm! Check out the full list by clicking here.