I’m pretty sure they are going to do the opposite, support server-to-server, and never support client-to-server. They have been meeting with the maintainers of Mastodon and admins of large instances. Their stated goal is to allow migration off without losing your social graph (this is obviously a lie about motivation, but that’s not what I’m taking about here). This is all about server-to-server implementation.

So, they are going to be part of the server-to-server Fediverse, and keep all of the juicy app data from Threads users to themselves.

Yes, plus if they support client-server then kill it later, they risk the same kind of backlash that happened to Twitter and Reddit when they killed third party clients. But if they only support server-server when they kill it, they can just send an email to all the geeks telling them "import your account into threads by X date!" and most "normal" users will never notice

Supporting server-to-server ActivityPub is slightly risky for them as it gives people an alternative, and there will always be outward bleed. On the other hand I think it takes a lot of pressure off potential legal troubles around being a monopoly (which they must be worried about if they actually manage to kill Twitter).

I predict if they manage to be the overwhelmingly dominant platform in the Fediverse, they’ll keep it working. If they see another big competitor jumping in and taking a lot of users (or hell, if Mastodon starts to eat their lunch), I’m not so sure.