Excellent post, and it is truly heartbreaking stuff. We know Eugen signed an NDA with Meta which just seals the deal for me given the other refusals to answer basic questions. I think he is probably a person who is finding validation for something he's worked on for a very long time, and Meta is blinding him. But that's what they do. They are emotional manipulators by trade.

Mark my words, this’ll be the end of Mastodon especially when Meta can outspend Mastodon all day every day to add proprietary functionality

This is exactly what happened with RCS. Sure, it is an open standard. But Google EEE'd it by adding proprietary functionality using their near unlimited budget and influence, then built it all around their own proprietary middleware, like Jive, to lock out others. Some of the most popular messaging apps, including Signal, had been begging Google for RCS access for years. Google refuses, because they firmly control it now. Only a handful of partners get to access the supposedly "open" standard which Google has co-opted. Sure, you could pour resources into the old, unmaintained RCS standard from over a decade ago. Before Google essentially killed it by moving proprietary and snuffing it out. But then it wouldn't work with Google's RCS, and Google's RCS is what people know as RCS at this point.

Meta will do the same thing with ActivityPub specifically, and decentralized social media in general. They will EEE their way to the finish line. They will wall it all off and prevent account portability and cross-communication outside of a preferred partner network. I could see them walling it off to the Meta-owned properties as they seek ways to further tie Facebook, Instagram, and Whatsapp together under a common protocol which they've EEE'd.