well, thanks for clarifying the movie release date, i'd forgotten. but with that knowledge, i just don't see the expansion releasing anywhere near the movie.
but anyways...
alpha's are usually a closed door, internal test, that have very specific stability test goals in mind, especially for new features.
beta tests are when you invite members of the community to come and help test things on a larger scale and ensure that the server hardware is capable of running the new features - take garrisons at WoD launch as a prime example of failure to load test properly.
before you question my statement, do some research -
https://en.wikipedia.org/wiki/Softwa...ase_life_cycle
the fact they are inviting people to test alpha and that mmo-champion is posting alpha updates on it's front page should worry you. it implies that blizz either have such grand plans for the expansion that they are months behind in development, or they're just months behind anyway and as such, the only way to keep the hype train rolling is to attempt to publicise through community websites - aka the curse network, all the exciting things that are happening in ALPHA. not beta. not release. ALPHA.
Warlords of Draenor was designed, and the content release schedule for it, was paced around the idea of yearly expansions - a promise blizzard have been trying and failing spectacularly to keep to for the last 5 or 6 years. there's no more content patches due for WoD and players are pushed through each tier of content so fast you can reach endgame within a couple of weeks, which is not conducive to a MASSIVELY multiplayer online game - in fact, it's shrunken the relevance of anything outside the current expansion into obscurity, which makes for a very short player experience.
whilst there's a world of content out there for any new players (lol) to explore, for anyone else who has already played through that content, the game is no longer worth the price of the subscription.
i imagine sub numbers will spike again once legion is released, then drop off again soon after. player retention is at an all time low. hate to say it, but WoW is entering it's final days, it's not dead and will probably thrive on a low population for a long time (if they handle server populations better), but it's heyday is long gone.