Usually these expansions come in 2 year cycles. We’re base game + 2 expansions and six years. World of Warcraft, Burning Crusade, Wrath of the Lich King.
The 6th anniversary message from Blizzard to the characters, found in the mailboxes this week, promises it will be an interesting year. “Year.” Not “Couple of years.”
And we are only getting half an increase, 5 levels rather than ten.
So, that tells me the next expansion will be this next year, when we go from 85 to 90 in the Emerald Dream. (Though apparently maybe Stormrage resolved all that Emerald Dream business in a novel taking place between Arthas and the Shattering without our knowledge, at least those who haven’t read it.) So who knows what will be coming at us.
Which then ultimately leaves players going from level 90 to 100 fighting the Burning Legion across the universe. In two years time.
Just me speculating.