Yessiree (holy crap, spell check accepted that!) the "Alpha" really has been an Alpha, and in the last couple months before Legion launches, Blizzard will be opening up the "Beta Test."
Basically, their reasoning is that these days, if you call something a Beta, people expect a polished demo of the game that they can play ahead of time. Obviously, that's not the case, and of course kind of invalidates the purpose of a Beta (except for marketing purposes, which to be fair are substantial.)
The good news is that if you've been waiting to try out Legion, I suspect that the invite waves are going to be far larger than the ones for the Alpha. I know that I'd really like to try out the Demon Hunter and the other major systems for the expansion before August.
The bad news is that this does kind of shift the goalposts. How long before people are going to expect "Alpha" to mean something polished and ready to go.
To be clear, Legion is not completely finished (and we already have a release date, so its state of finished-ness is kind of moot, barring some shocking lack of progress over the next 3 months.) And I'm sure there will be bugs in the Beta to sort out.
For those of us who actually like to get in there and give feedback during these tests, this is a little disheartening. I feel like good feedback on Brewmaster Monks turned an awkward spec where you would literally spend some of your time not even able to attack enemies as you shuffled to avoid attacks into one of my two favorite tanking specs.
Then again, during the Beta for Warlords of Draenor, they utterly ruined Arms Warriors despite all our protests (something that I think Legion might be bringing back from the pit of horribleness.) So perhaps my sense of power as a tester is inflated.
Still, given that we've got the whole summer to wait for Legion to come out for real, I certainly wouldn't say no to getting an early look at the expansion.