Here is mine,
Release Date: Legion is ready to be released today (the discs are printed, the packaging is wrapped, and the trucks are ready to roll).
Reason Why its Believable:
1) Blizzard does not want to have 2 games being released at the same time and they have to release Overwatch due to platform gaming console agreements,
2) Blizzard has said that they increased the size of their development team (and there is also no content work being done on WoD) so it is conceivable that they really are getting a lot done (but they are unwilling to show it),
3) "If it aint broke why fix it?" Blizzard had made their money through a very repetitive business model: hype and time. The more hype for the game and the longer people have to wait to play it has always ended up in major $$$ for blizzard.
4) There is no compelling reason to release the expac right now. There is a core group of players who will always stay subscribed no matter how long they go without adding content and blizzard can always increase their revenue stream by selling a highly desirable mount in their eshop.
Sound reasonable?