For all of us who have been playing a long time (since BC or before then) and signed up for the pass on the first day, we are probably going to get in the first wave. Emails just haven't all gotten out yet. Their system may still be sorting who should be getting invites.
Got the AP on day one, and have been playing since vanilla (with a handful of 1 month breaks over the years). No invite. Is there anyone who HAS had a break in their account who has actually gotten an invite?
The servers aren't up yet, but when I checked my battle.net account, the MoP Beta link was there under games. I've got the install file downloaded (waiting on servers) and was able to queue up a character copy to Gilneas (US) - one of 2 US Beta servers (other was Lost Isles).