As it is now, no. The beta team was determined months and months ago, before any builds of MC12 were publicly available.
However, this does not mean you will not receive updates to your version of MC12. They will still be releasing builds of MC12 to everyone (JimH indicated likely weekly) after they have been initially tested by the handful of us on the official "beta team". I'm not sure, but I'd guess the reason they are trying this is to give them more flexibility to try new things with MC12 without having to worry about people screaming to the effect of:
"OMG! It broke my files and deleted my library and OMG I paid for this and it's crap!"
Its somewhat like Mozilla's model of having a trunk and a branch. The trunk is really bleeding edge stuff. No guarantees are made that it won't format your C drive, burn your breakfast, and kill your dog. The branch is a little calmer (but still actively developing), and might still do all those things, but probably won't.
The problem was that MC12 is quite a bit nicer than 11.1, and so a lot of people really wanted "in". This was allowed, but it somewhat unintentionally "tied their hands". People have an expectation that if they paid for something, that it should work reasonably well (and not delete files, force them to rebuild their libraries, or disable significant functions of the program). Some of us, however, have demonstrated over time that we have the time and inclination to assist with these "dangerous" builds, and so they will be releasing the "semi-daily" completely untested builds to us. After we have determined that they don't actually kill your computer (or dog) then they'll move those threads over to the "regular" MC12 forum.