I hate to be the one to shoot this down, but everything ive seen on every forum so far shows that random opt-in invites have not been sent out yet.
Wow forums would be flooded with screenshots, and so far its only people making j/k posts.
This may work in the long run. But blizzard could have this email blacklisted for invites, and we don't even know yet if the beta opt-in on the regular blizzard site can get you an invite for the Wow beta. Because it dosn't specify which game your opt-ing for and one would assume the interested people on the Wow site would have first dibs.
Methinks someone made most of his post up, even if it is a good idea.