Ah, I thought you meant more as in selling user data for ML training purposes or advertising.
Meta can still do it if even one mutual server has agreed (been paid) to federate to both platforms.
I dunno, maybe I'm too pessimistic but I don't see a way this ever works out in our favor, there will always be someone who doesn't care and just wants all the content. Just look at people being unable to get off reddit or twitter right now. When faced with a choice between sticking with 10% of the fediverse blocking meta, or 90% federating with them (since meta is probably going to be huge just by merit of being backed by billions of dollars), all their friends and companies and communities being on meta sites, there is no way they will choose to isolate themselves. It's how sites like reddit gained a monopoly in the first place, people just look for convenience and everything being in one place.