Every single expansion has been announced at a Blizzcon. Furthermore, every second Blizzcon has had an expansion announcement, and every expansion has launched 9-12 months after its initial Blizzcon announcement.
So let's assume for a moment that they don't announce 9.0 this year -- this would, of course, mean that they'll be announcing it next year. Assuming that 8.3 drops before Blizzcon (which is very possible), that would mean almost 2 years of Ny'alotha. If you'd spent any length of time thinking about this, you'd have known it to be a ridiculous scenario.
Afaik ICC wasn't out before Cata was announced, and the same was true for Dragonsoul and MoP.