This might be an unpopular post but so’ll be it: Mastodon is the existing proof that Meta could kill Mastodon any time.
Mastodon was using a protocol compatible with GNU Social: OStatus, but some features were quickly added without consideration for other implementations.
So when per-post privacy were introduced, for example, they were very public on GNU Social, because their devs had no idea this was coming. And GNU Social was blamed for it.
Instead of having more users, GNU Social is now (almost?) dead. Of course it’s not just because of the above. But it wouldn’t have been set back so much without Mastodon.
Now, Mastodon is opensource, has more features and some compatible implementations. I run Pleroma myself. But why would one think Meta could not cripple them both?