I prefer MK doesn't collide with any universe.

Mortal Kombat vs DOA or

Mortal Kombat vs Tekken

Mortal Kombat vs Street Fighter would had been stupid cause the MK characters would have to be cartoon looking, lol.

Mortal Kombat vs. Spy Kids

They should have added Grimjack. He's the MK-type.

MK vs. Spongebob and Friends

I've always thought the Mortal Kombat and Soul Calibur universes would meld together quite nicely.
Cervantes Vs Scorpion. Undead Pirate Vs the Ninja Spectre
Shang Tsung Vs Nightmare. Soul Suckers Anonymous.
Lizardman Vs Reptile. Battle of the characters with the most unimaginative names.

Plus some of the Fatalities. Ivy wrapping her blade around her opponent and BAM! Human cold cuts.

Oh it looks so beautiful in my mind.

To be honest though, if they were going for a crossover. Mortal Kombat Vs The Batman Cast would surely have been better than MK Vs DCU.

Purely because, thanks to Three great Batman movies and the fucking excellent Batman: The Animated Series, even the most insignificant Batman villain is more well known than some of DCU's "Top Tier" Heroes.

I would love Soul Calibur vs MK. As long as Midway had no part of it.