More freely available content would be great, wouldn’t it?

I doubt most people moved to the fediverse simple because of better content. Personally I didn't. And quantity doesn't mean quality.

And certainly they are likely to be data-hungry greedy shit, but there is a chance that they are actually good ideas - there are actual people working at meta after all.

Contributions are open for these people. But the moment the contributions are facilitated through Meta, they represent Metas business interests.

What are the downsides?

Control. Meta could swamp the fediverse and just because its open source the current platforms wouldnt necessarily continue to exist in the same way they currently do. We could see even bigger fragmentation or breaks, some Admins might feel forced to federate with Metas service, leading to the currently existing community breaking up.

But maybe, just maybe, goals align here, and Meta can make money and improve the Fediverse and the Internet with it.

Imo the last years has proven, without a doubt, that those things simply do not align.

To conclude: We have seen these things before and they havent ended well. People here seem to undererstimate the power Meta has and the impact that this power has. Even if all current instances were to defederate from Meta, simple association, user demand caused by an influx of Meta users and hard to guess power dynamics would make the fediverse a far different place than it currently is. To make a comparison: you cant drop the gravity well of a black hole into a small, complex planetary system and expect it to be unaffected.