You're forgetting Wilden. Its only the 4th race that is in any doubt. DS races would really not make sense to put in the PHB3 IMHO. Its DS specific material. Each of the other settings has a race and a class unique to it. DS may need 2 of each, given how much it varies from 4e default setting concepts. OTOH its possible they may put one of them in PHB3 since you'll probably need it anyway to run psionics. Who knows?
There are plenty of other candidates for the 4th race though. I expect it will be a retool of something from previous editions, but it could also be totally new. Speculation is free, and there is plenty of it. They may not even have decided themselves yet. That book is still a long ways off.