To tell the truth, I'm a little disappointed. I've got a beta key from BlizzCon, but I've already signed up for the Wrath beta through the usual channels. Of course, we still don't know how this works -- maybe those with a key will be given access before those who just signed up randomly, but it sure seems like everybody will get in eventually. Which means that even if you didn't get a key at BlizzCon, you'll still get into the beta anyway. I thought that Blizzard would have treated those who came out to their event a little better (and, at the very least, been a lot clearer about how registration for the beta is working -- are they making it up as they go along?).
But on the other hand, the open registration just means more people will get into the beta, and I don't have a problem with that -- the more the merrier. As always, the problem with Blizzard is communication -- it's fine if they want to keep which beta these WWI or BlizzCon keys are for a secret, but when the beta registration actually starts, they should make a plan, stick with it, and let all of us would-be beta testers in on what it is.