Myself, what I would like to see would be aliens that really look alien, and what I mean when I say that is that the existing alien races tend to fall into the "people dressed up in costumes" type of look, very human-like in basic shape, with mostly joints in the same places that bend in the same directions. It would be nice to see some races introduced where if this game was a big-screen film production or movie, people in the audience would be impressed and think "Wow, there's no way that alien could be some actor dressed up in a costume and make-up! That...thing really looks alien!" Heck, most of the alien races in the game are even human-sized right now!
I have to agree, after playing numerous times, it would be nice to see more races, and some randomization with what comes first.