We'll end the public beta when either a large wave of major features is added or we have new scripts for testing. Then we'll test any new features and scripts to make sure everything is working properly enough for a public beta.
We actually do test newer builds privately, but not in large, organized private tests. Rather, the few of us that happen to be available when a new major build is ready try it out on a private server, and if it looks good, we push it publicly.
