Return to Karazhan kind of implies I've been to Karazhan even once. It's like when you meet someone new at a party and they say "So good to see you again!" and you have to decide whether to tell them you've never met or just go with it, trying to work out who they think you are and generally besmirching that other person's reputation. Oh hang on - is it about someone ELSE returning? ANYWAY let's ignore that awkwardness and talk about World of Warcraft [official site] Patch 7.1 and the fact it's going to launch on 25 October.
So, a bit of context/info to start. 7.1 is the first major content patch for the Legion expansion. It'll bring with it this five-person, Mythic-only Karazhan dungeon, plus a new raid in the form of Trial of Valor.
I don't often watch/listen to WoW Q&As in full because I don't play so it soon gets jargony or I'm marooned from context, but I enjoyed the early part of this recent VOD because of how WoW game director, Ion Hazzikostas was talking about class balance. Then it gets SUPER-jargony and people are talking about mythic gubbins and builds and so on, then at about 52:50 is when the Karazhan talk starts.
The patch should arrive on 25 October (26 October for EU), so pre-Blizzcon. It'll bring with it the Karazhan dungeon which you need to do an attunement quest for, but Hazzikostas was saying that it was more for context so it would likely be an account-wide unlock from that point. The Trial of Valor raid is scheduled to unlock a fortnight after the patch releases to a) not force players to choose between raiding and watching Blizzcon (probably a sound business choice on Blizzard's part as much as a player courtesy) and b) because it's hard to offer game support/make emergency tweaks and bug fixes while pretty much your entire staff is at Blizzcon.
So yes. Raid after Blizzcon with three bosses; Odyn, Guarm and Helya. Helya. They called a boss "hell, yeah!"
Here end my relevant observations.