Midway's official MK: Deadly Alliance website revealed an important gameplay detail on its launch today. MK:DA will feature a "multiple-move-set" fighting system. Conceptually, the system will feature fighters with more than one set of moves, contrary to all past MK games, which can be changed during the course of the match. Whether the sets can be changed in the middle of the round or only before and between is not detailed.
Certainly this is a huge change in gameplay, and will definitely have a bigger impact than the RUN button or weapons ever had. Keep your eyes open for more details on the multiple-set system as it appears to be the centerpoint of the new gameplay system in MK:DA.