Haha i was gonna ignore it but i totally agree with you. That sounded terrible!
New engine means they would have to port the whole game to a new engine. That would take years. Zero chance that would happen. Everything would be started from scratch with a new engine. Which is why they won't do it. It would go the way of every mmo sequel and not be the game that people wanted. WoW2 is simply a bad idea and likely doomed to fail.