If I'm remembering correctly, the soundtrack for the last one was released just as the the movie opened for general release, so it might not be unreasonable to suppose the same will happen this time around.
I don't recall what the lead time was last time for advance purchase, but the DVDs and Blu-Rays for
Into Darkness are still on "Sign up to be notified when this item becomes available" status. I expect that'll be changing pretty soon.