based on Baker's recent blog post and other info that has come out, it looks like we will get all three of these races in DS! Is it safe to say that all the other races are out? Without a new class, there is a lot of room...
Well, those are the "main" races, they can add others in as Draogn mag articles? 
Those races are required t play Dark SUn, pterrans, aarakokra etc, aren't "Needed" and add some problems (like flight)
half-Giants I just hope are Large and they work out how to balance that. Medium sized halfgiants is a bloody oxymoron! lol ;)
I can see Half-Giants following the Goliaths; very tough, and on the cusp of being Large, to the point where they can have Reach/etc. The main thing they always have to watch out for is Large weapons being weilded one-handed.
Muls could easily take the place of Half-Orcs; human-height half-breeds who are very tough, very strong, and built to fight.
The Kreen though... that's going to be interesting. I wonder if they'll still have the over-powered "only needs to drink once per week" and the "can weild 4 weapons".
Well, since there's already a race that doesn't need to eat or drink at all, I'm not entirely sure that they'll balk on that front.
And on the weild 4 weapons front ... they can weild as many weapons as they like, but they can only use one, maybe two of them in a round. Depends on powers. All they get for having two weapons in hand is to avoid spending the actions drawing and sheathing weapons so they can use something different. Hardly overpowering.
Going from two weapon fighting, a multi limb weapon fighting feat would only allow extra damage on hits, currently Two Wepaon Fighting gives +1 damage, so, multi limb may give +1 per extra weapon over the 1st? ;)
I would hope that they would put more than just the standard Thri-Kreen in the game. The Thri-Kreen of Athas supplement from way back was a favorite of mine. But I'm sure that due to space limitations they will just do the original Thri-Kreen. Maybe we'll get an expansion on them in the MM3.
I'm still wondering if they'll replace the Half-Giants with Goliaths. I hope not, but I have heard that rumor.