I think it is a possibility.

Mortal kombat games are known for hidden secrets,references and lately cameos so why not? I think there will be easter eggs. there is already the pig in the "Outworld market" stage, that NRS are already saying is that the same pig? who knows?

Maybe in a background of a city arena have A'Zreal from Batman on a rooftop looking at the battle.

Road Runner animality for Kabal where he loses Wile E. Coyote (again), forcing Wile E. to compensate by eating the opponent, if animalities return. If not, it can also be a fatality for either him or Shang Tsung.

Kabal could also get an alt based on the Road Runner, where the respirator resembles RR's beak, the upper mask the rest of RR's head, feathers on his behind, and boots resembling his feet

Queen Mary Stuart (Reign) in any backgrounds with a throne, or as a part of a friendship for royal characters like Sindel, Kitana or Goro.

Stop.

This kind of thing would seem more appropriate for an actual crossover title.

No....just no.

Would like to see Raizo from Ninja Assassin.

You already saw The Joker in MK2011's Pit Bottom.

I don't think so. Lets save it for a crossover.

Sam and Dean Winchester 4 gest karacters.

Lobo's hook chain and shotgun laying in the background. That's about how far I would want it to go.