Any instance can choose what other instances it interacts with.

Per instance

Due to the dominance of just a few companies' big email services, it's now almost impossible to set up an independent email server. Emails from small independent servers are just not delivered by Gmail and the like. They will only accept emails from other big email providers. In this sense it is a problem that Google owns the most popular email instance. They and a few other large companies have effectively turned a democratic and distributed system into a closed loop owned by a handful of big corporations.

The real fear is the embrace extend extinguish. IE if meta encourages people to join their instance, then gradually makes things incompatible after major communities move to them

Kind of like how Facebook Messenger (and GChat, and AIM) used to federate with XMPP, and then dropped it like a bad habit once their platform took off.

I think it is really important for communities to spread out to avoid exactly this. Users can centralize, but distributed communities is what will prevent what you describe.

My bigger worry is that they'll try and take control of the fediverse on a larger scale. Even if all of their users join the fediverse and it becomes less convenient to be defederated from the larger corporate instances you can still have accounts on smaller instances or your own and you'll be able to completely block all the corporate instances. But what if they strike a deal with activitypub? From my knowledge they're the backend of the entire fediverse. If they're able to do what they want with the fediverse as a whole then where do we go? I think that the developers of activitypub would be against that but meta can spend as much as they want to take control of this and I don't know the developers personally so I can't be sure if they'd pass on that money. I might be worrying a bit too much but big tech has a long history of taking stuff over like this.; social media and e-mail are both great examples of that.

It's funny you bring Email as an example because everyone using the same 3-4 providers effectively centralized email. Anyone who tries to run any self-hosted email with decent volume quickly discovers this fact

currently you lose everything. I'm hoping they add a transfer tool like how masodon(i think it was that) has with transferring accounts

Transferring is theoretically technically possible (Mastodon does it), but Lemmy hasn't implemented the option yet. There's an issue for it on their GitHub.

Why would Facebook bother buying out existing instances? They have the resources to create thousands of instances, and the userbase (the idea is to migrate all Instagram accounts) to populate them.

Not to mention that they're creating a Twitter/Mastodon clone, not a Reddit/Lemmy one.

I think instance admins do care

Maybe. But then the instance they purchase is sealed off from the rest of the federation and a large portion of the users jump ship.

That's like saying they're "in talks with HTTP". ActivityPub is a protocol. It's an open source standard. That standard is currently under development by the World Wide Web Consortium. There is no "ActivityPub" for them to be in talks with.