Figure it might be too soon to start asking about this, but I'll give it a shot.
I'm interested to know how you're planning to handle the Blackwing Lair release. I do believe Blizzard released both the attunement and the raid on the same day, although I can't recall exactly how it all went down. Regardless, unlike today, the majority of players back on retail vanilla did not have any idea where to start the quest to get attuned or what it involved doing. The patch notes from 1.6 state there's a quest for the attunement, but leaves out the whereabouts and the objectives.
I believe if you choose to release both at the same time/day on Nostalrius, you'll create a situation where you've got 10-20 guilds or even more, all trying to claim the tag on the Scarshield Quartermaster at once, probably resulting in an overall shitty experience for everyone involved. Though I could be entirely wrong and most guilds will just head for the route through UBRS, which besides being inconvenient since you can only enter with 10 players at a time, is perfectly doable, though not very fun if you wipe without any way to recover.
Even if my concern above turns out to be obsolete, I still believe a better solution would be to implement the quest for the attunement some time prior to BWL opening, and as for the actual raid release, try to compromise and land on a somewhat neutral time so most EU/US guilds can have a go at it regardless of their time zone, and be able to start BWL at roughly the same time on the opening day.