Nope. If this expansion will try to bring the TBC crowd back it'll fail, hard. Almost all of my friends who played during TBC and quit after/during WotLK said they didn't have the slighest interest in this expansion, and have moved on.
My guess is back to almost 8 million for a short period, then starting to decrease again. Maybe stabilise at 6 million in the middle of the expansion, and ending it with around 5 million.