I'd like to see Arkanians (And possibly Arkanian Offshoots, maybe pureblood arkanians for the Empire and Offshoots for the Republic?) because, unlike Togruta, Nautolans or Kel Dor, they weren't invented for the prequels but rather have played a big part of the Old Republic era EU material ever since the 90's.
Tales of the Jedi and Knights of the Old Republic comics both had central Arkanian characters - the same is true for Miraluka and Cathar. And unlike the tentacle-heads (Togruta and Nautolans) and the Kel-Dor, the Arkanians actually have an established cultural identity, power base, political alignments and history, rather than just being popular because of random cool-looking Jedi in the prequel trilogies.
As for which ones I THINK will be put into the game, Togruta, because fanservice demands more sexy tentacle-headed rainbow-skinned girls.
Wasn't Kit Fisto a Nautalan? And I don't remember him being from the prequels, but I could be wrong.