Gotta say that MK1 Raiden and MK1 Sonya are tops on my list for characters that haven't received any Retro Love. I loved Raiden's cheesy little white suit. Seriously. Lots of love for that one. Also, Sonya needs a costume that doesn't make her look like a whore.
And just for kicks, fill out the rest of the MK1 roster with their original outfits. Short-hair black pants Liu Kang, white outfit & flesh-colored sneakers for Kano, plain black shorts for Johnny Cage. then I can have my dream MK1 tournament in the courtyard stage
From there, I'd love to see a quick fix of MK2 outfits for the rest of the male ninja - esPECIALLY Reptile (and I think they've already done MK2 female ninja from that old costume list I read during the MK9 demo days. Only a matter of time on those.)
What else...Oh! MK2 Shang Tsung would be a real treat (dat hat.)
Slightly off subject, but I'd also love to see some more stages. Again, the missing MK1 stages (Castle Gates and Warrior Museum,) the missing MK2 stage (bridge/thing with the spikes on the ceiling,) and an MK3 stage (I'd be happy with either Pit III or the Spiral Vortex stage.)
I'm a needy little Mortal Kombatant
But MK1's gotta have the priorities, I think, on all accounts. You want retro, then I say go
all the way.