If Facebook behave and their instances have good moderation, they'll be successful. If they don't, they'll get defederated and turn into some niche twitter clone echo chamber like Truth Social.

Facebook is a company with great open-source tech contributions (React, GraphQL) but absolutely awful products (Literally every social media thing they've got their hands on), which is why they are desperately trying to turn their side project Oculus into their main product. And I think they, as the original "The Social Network" company, see the writing on the wall: that they either embrace federation and decentralization, or get swept away by it into the footnote of social media history.

Now, I don't think Facebook wants to JUST run an instance where they get to control everything. I think the most likely scenario is that Facebook will offer easy managed federated instance setup hosted on their own cloud servers for less tech inclined individuals and companies in the future, and they'll rebrand it as "the actual metaverse", which will finally end their tenure as an advertising company.