https://us.battle.net/forums/en/wow/topic/20753227153
Q: Raid testing already? Only a handful of guilds have even finished Mythic Nighthold! Are you out of your damn minds?
A: We realize this is coming right on the heels of plenty of raid content on the live servers, and that competitive guilds feel like they need to get every bit of exposure to upcoming content in order to be properly prepared. It's not ideal timing, but it's a consequence of the way we're structuring our content releases, and something we're looking for ways to improve and continue to refine over the course of Legion. As we've said in the past,
Tomb of Sargeras will not be available right when 7.2 unlocks, and a quest arc (akin to the 7.1 Suramar Insurrection campaign) will lead up to its opening. We certainly do not want to rush players through content faster than they can enjoy it - Nighthold is going to be the premiere raid for some time to come.
But Tomb of Sargeras, at least as far as art assets, and most descriptive text, voice overs, and so forth goes, needs to be in patch 7.2 data. That means we need to begin testing it far earlier, relative to the date when the raid will actually go live, than we have in past expansions.