Strictly speaking the common code in that branch *will* be updated but since we don't plan to make Linux releases off the branch it's easier to say "won't be updated" (or it just gets too hard to explain ).
The sequence of events is pretty well defined right now, since the remaining integration tasks pretty much have to happen in a certain sequence, so that's the sequence in which each of the new initiatives will transition from "science project" to "real". KMS/GEM/TTM first, then DRI2/RDR, then power management and Gallium3D work can happen in parallel.
No official dates, but we don't release official dates for new features in fglrx either.
I am fairly confident that ON BALANCE the open source drivers will make a larger chunk of our user base happy than fglrx would with reasonable legacy updates.
Improvements to 3D require big changes but a lot of that work is well underway. For me the big milestone was seeing Gallium3D merged into master; I agree that's a totally arbitrary and fudgeable milestone but I do have a lot of confidence in the people behind the decision.
Power management is easier by comparison, since the required info has already been released and the major obstacle is waiting for churn in the kernel to settle down so power management code can be built on top of all the other new stuff.