When we next run a beta panel - and I'm hoping we'll have news of that soon - we'll invite applications to join as before, via a forum thread. We're not accepting advance applications because that gets complicated. Rest assured that there'll be plenty of room for lots of testers, so there's no need to worry.
I'm meeting with someone in about 14 days, and I'll know more after that. At the moment I can't give you any advance information.