This was my idea.
The 5 realms will return, maybe with one possible new one. We will explore different parts of these realms this time. However, instead of one long quest with a single character, EACH character will have his own mini-konquest to complete in these same realms. These mini-konquests will help to tell the character's story up until this point, kind of like a playable-bio.
While this certain character goes through konquest, he has the opportunity to run and collect koins as normal, but he also has the opportunity to do his character-specific quests. Using that character will open up areas previously unaccessable. This character will have the chance to unlock certain things, such as that character's bios, alternate costumes, different fatality, hara kiri, and weapon upgrades (if they decide to do that). Finishing this character's konquest could unlock something as well, such as a friend/foe character or one of the above mentioned items.
After that character is done, move on to the next one.
You can always return to Konquest with any character to go back and do some training missions over.
Training missions: There needs to be a few more of these, with different match stipulations. MKD was good, but it needed a few more..and you needed to be able to pick which character to practice with, not just randomly morph into a different one after you beat Konquest. Some of the training missions could be insanely hard (much like the Shang Tsung one in Netherrealm), but well worth the reward (something other than a few koins).
Hidden missions: There would be many hidden missions in the game, unlocked after you complete a task. For instance, say you completed Konquest with Scorpion. Then you went ahead and did a Konquest with Tanya. Somehow Tanya helps Quan Chi in her Konquest and you can see him walking around now. No hints would be given as to whether this is an additional mission now, but the player, knowing that Scorp has a thing against Quan Chi, could go back, pick Scorpion, and look for Quan Chi. A fight could happen, in which if defeated, Quan Chi would drop an unlockable. Now a lot of these hidden missions would not be this obvious, but I think you get the point.
I had more, but I am tired and cannot think, as usual.