Funny, Mastodon just posted a similar thing about creating a foundation. But the problem is, the existence of a foundation does nothing to prevent billionaires from controlling social media. For billionaires its very easy to donate a few hundred thousand USD to the foundation and gain influence that way. I expect that Bluesky will be fine for the first years (maybe like early Twitter), but sooner or later the foundation will take decisions that the users dont like, and there is nothing they can do about it.
In my view, the only way to avoid influence from billionaires is to avoid any large centralized structures. In the Fediverse there are dozens of platforms and thousands of instances. Even if a billionaire were to take control over a couple of projects or large instances, people would create forks in a matter of days. Some admins would block these corrupted instances, and their users would barely notice that anything changed.
So Bluesky is just trying to repeat something that has already failed. The Fediverse is the future, but it will take a long time for most people to understand that.