In the core rules we have Terrans, Taurans, Andromedans, Rigel, and Daelans. I added the Daelans myself, but I think they will probably not make the cut after playtest just because I want to make room for the addition races from our IndieGoGo backers. Also I want to keep the Prelude brief--my goal is to have the background info and politics brief so it doesn't bog referees down in perceived setting obligations. I personally find that overwhelming, and frankly I think it is one reason Prime Directive has only enjoyed meager success. There is just too much background stuff to keep track of.
It has been mentioned that the Zangids would make a good PC race. I agree, but in the core rules I would like to keep it to the aliens who are members of the Confederacy only. Keep in mind the Rigel are essentially Zangid/human hybrids. If we make Zangids a PC race in the core rules it opens a can of worms to detail the way Zangid Empire classes may differ, etc. and I think I'd like to reserve that for an expansion.
What about other hybrids? Naturally people will want to make Tauran/human hybrids. In Star Trek, aside from his emotions, Spock functioned basically like a full Vulcan. Should we add Half-Taurans? If so, I think that would be the only hybrid I would want to add to the core rules.