So there's good news and there's bad news: The good news is that Legion's release date has been officially announced, which means that we can now purchase it in good conscience, knowing when said purchase will actually be available. The bad news is that it's way the hell over at the end of August, which means a few things:
First, even with the rather thorough Alpha testing we've seen, there is actually enough time for a whole Beta test between then and now. Second, it means that the whole "advantage" of having only two raid tiers for Warlords of Draenor (something which I wouldn't even consider an advantage, given that even if the expansion were coming out now, we'd still have had a pretty damn long content drought) is utterly null, because this means we're still going for something like thirteen months between major patches (only one less than the post-Mists drought.)
For most games, this wouldn't be too much of a problem - in fact, taking a little longer to come out with the next Assassin's Creed is probably a good thing - but WoW is A: subscription based, meaning that we're paying for all those months of non-content and B: it's multiplayer, so the more people who give up and stop playing, the less enjoyable the game is for the players who are online.
I've been on a WoW-hiatus for a while, and I was looking forward to getting back into the game soon. But apparently it'll be another four months (maybe slightly less, given the pre-patch.)