Fact
Per Icy Veins' summary of the Oct 8 WoW: Forever podcast: the new raids will not have an attunement process, though some may need players to bring specific items to get in (like dousing runes in Molten Core); at launch only Onyxia's Lair has a traditional attunement. Update (2026-10-11): Warcraft Tavern's account of the same podcast (at 53:33) agrees and adds detail: Onyxia's Lair keeps its long Classic attunement quest chain and the attunement is not account-wide, at least at launch; Barrow Deeps and Hyjal Summit need no attunement chain, though the developers hinted at extra steps to 'get the full experience'.