Since there will likely be a next gen game that is NOT a fighting game next year (similar to how MK:SM came between MK:D and MK:A) I got to thinking what it could be, and with the recent problem of the plot disasters caused by MK:A in no way, shape or form even attempting to be explained in game, I had a thought.
What if the next MK was an action-rpg along the lines of X-men Legends and Marvel: Ultimate Alliance. These games have you control a collective of fighters in a party (usually 4). This system works well with extensive storylines (play XML and you'll understand) so i could see such a game working with the MK franchise to fill in everything from Pre-MK I to the cannon conclusion of MK:A.
You could play through from different perspectives also, such as the Earthrealm defenders (Liu Kang, Kung Lao, Raiden, Johnny Cage, ect.).
This game could replace/confirm/clear-up all cannon. It could also introduce some new characters for MK8 and set up the story for MK8.