Isn't there some blue post floating around somewhere that says were due an announcement in February even though Blizzcon got cut? That seems the most likely time for it to be dropped in my opinion. Drop a big trailer with some attention grabbing details that will keep players strung along for the next 4-8 months of content drought after the last patch is dropped. Maybe put the main selling point out front and center to really drive it home with a promise of things to come in the prepatch (kinda like they did with Allied races in BFA prepatch).