There should be two single player modes available. One should be the general tournament mode as usual. The other one should be character specific i.e. the enemies in this mode should not be random but related to the selected player. Like if I select Sub Zero in the tournament mode then any one can fight me like even Jax who has no connection with SZ. But if I play in the Campaign mode characters like Quan Chi and Scorpion etc would only be allowed in a proper hierarchy so that the story unfolds. Another thing that can be done is that some hidden characters can be brought into focus in this manner. Like Smoke (human) can be there in Sub Zero campaign but not in the tournament mode.
This will allow several uncovered topics to be covered up by the developers like what on earth happened to Reiko.