I think they're going to rush to put out a release pre-August 28th, just a thought.
If they release post-GW2's release, I think they'll take a (rather large) hit to subscription base. GW2 already has over 3 Million bought - has no subscription fee - and competes in the same market. I don't expect people to pick up two games around the same time - so I really expect Gw2 to swoop up a lot of subscribers from WoW.
This is nothing but speculation, but hey it's a speculative thread anyways. :P