Meta can introduce their signature rage farming to the Fediverse. They don't need to control Mastodon. All they have to do is introduce it in their app. Show every Threads user algorithmically filtered content from the Fediverse precisely tailored for maximum rage. When the rage inducing content came from Mastodon, the enraged Thread users will flood that Mastodon threads with the familiar rage-filled Facebook comment section vomit. This in turn will enrage Mastodon users, driving them to engage, at least in the short to mid term. All the while Meta sells ads in-between posts. And that's how they rage farm the Fediverse without EEE-ing the technology. Meta can effectively EEE the userbase. The last E is something Meta may not intend but would likely happen. It consists of a subset of the Fediverse users leaving the network or segregating themselves in a small vomit-free bubble.
Here I am assuming they would show up as users when FB's version shows up as an instance and can be delt with on that level. I am just starting to get used to this federated stuff.