The one thing that I suspect will be missing is new players. One of the things I enjoyed the most was seeing in chat a player that didn't know how to get from Iron Forge to catch a boat to the other continent, and I'd have fun showing him how to get through the Wetlands to the port. The Wetlands was a higher level than we were at the time the quests wanted us to visit the other continent, so it was a dangerous journe…
I like how everyone conveniently forgets that hundreds of millions of gamers never played Vanilla WoW.
Everyone does not know the game like the back of their hand. I have tons of friends who missed Vanilla and she's looking forward to playing it for the first time.