There are different betas. I assume you mean the 8.2 beta, as that is what dropped today. Content creators have acess to a separate beta all the time that has different features. The story quest betas give access to specific new content and have a lot of limitations on changing your roster. Kabam sends out invites to specific accounts in advance, and as far as I know there is no way to sign up for them. It seems like experience in past betas makes you more likely to be chosen, as I have been for a lot of the most recent ones, but not always. While cool, you're not missing out on something huge or gamechanging. Just a couple limited-time interesting interactions and the ability to give feedback on new content.