And now I’m commenting from a lemmy.world account because Lemmy from Mastodon has some rough edges like the need to tag the community in my comment above to ensure it actually reaches the lemmy.world server.
Tumblr and Flickr are also talking about ActivityPub support, but it’s not clear if or when that will actually happen. It would make more sense to me for those services since they’re fairly small and it’s a way to substantially increase the possible audience. It’s not clear what Meta’s motivations are here, though a motivation some have proposed is that they’re trying to get in front of potential regulation. The EU Digital Markets Act, for example requires some services to interoperate with competitors, and having one of its new products join an established standard protocol is a way to say “you don’t need to regulate us, we already do the thing”.
I don’t think their blocking of comments mentioning Pixelfed is intentional. Pixelfed is not popular enough for Meta to care about as a competitor, and blocking mentions of competitors has never been among their tactics.