The ramblings on warseer from the more reliable individuals (of the disgruntled GW employee sort, or from those who took some pictures or talked to people at a games day) say that the Dark Angels are due up in February, and GW is planning on another "Orktober" but we'll see. The summer campaign is for Fantasy, so the reason we probably won't see Orks before October-ish will be due to the focus on that.
Dark Eldar are absolutely not being removed from the game, nor are the ratlings being pulled. A lot of experienced players have Dark Eldar armies. GW doesn't stock them in the stores because they know they're such ugly models for the most part that they wouldn't sell next to the newest Eldar sculpts, for example. Those of us who've been at this long enough know, respect, and in most cases fear a Dark Eldar army, and GW wouldn't dream of offending its most devoted players again the way they did when they nixed squats and Chaos Dwarfs for Fantasy (admittedly, I don't see the big problem with dropping squats, but plenty of folks did.)
Chaos is supposedly going to be broken up into two seperate books-- the first for the Chaos Space Marine Legions, and the second for Lost and the Damned-esque units such as Traitor Guard, mutants, daemon spawn, and the like. The two books are supposed to be usable both individually and together, much as the Beasts of Chaos and Hordes of Chaos books are for Fantasy.