If they decide to do an open Beta, I hope people are able to discern the difference between a beta and a Demo. People like to use the terms interchangably, but they aren't the same. A Beta will have issues, and will not function at 100%. This is because it's a preview of an unfinished product.
You can think of it as an unfinished recipe. Mostly there, but still missing ingrediants, so it clearly won't taste like the full thing. The idea is to find the bugs and glitches, and the different imbalances in the game, and provide real and useful feedback on those things.
It will be cool to have a public beta but I don't think they will do that. I was beta testing BF3 and I never liked it. It kind of killed the hype for me but I still ordered it but I seldomly play it.
I think 3Arch won't do a public beta but they'll drum up the hype to the stratosphere.