The XMPP ecosystem has federation, security and almost every client can talk to almost every server. If Moxie Marlinspike claims that interoperability does not work well in the context of instant messaging, I see this as him trying to manipulate the users so they do not judge him for his behaviour.

About Telegram: the fdroid version has no google dependencies, AFAIK

I did not know that blog post. However, it does not give evidence that Moxie Marlinspike is friendly to federation and third-party clients. If anything, it shows that he opposes open, interoperable protocols as well.

Moxie Marlinspike asserts that federation needs standardization and that standardization inhibits changes. He also asserts that protocols have to change to keep up with changing requirements. His unspoken assumption is that it is impossible to create real-world forward-compatible protocols.

While I agree with the first assertion, I strongly disagree on the latter two. Consider that protocols and data formats that do not have to change exist. An encoding like UTF-8 will probably never have to change to keep up with new codepoints. Also consider that forward-compatible protocols and data formats exist. HTTP seems to be a very good example for that.

I've been thinking about this a bit, and I think it would be possible to setup a non-profit, 'Federation Authority' (if you will), that could transparently govern a network of independent operators (that interoperate). Wikipedia works pretty well (IMO), and there would be an opportunity to iterate on their model (e.g. live web stream of board meetings).

I believe with enough traction, we could get hedge funds to give money while shorting the publicly traded companies that operate walled-garden networks.

N.B. I read your link when it was written originally, and have not taken the time to go at the issues raised point-for-point, but I'd like to see more efforts made in the direction I mentioned above.

Edit: The protocol has to have federation built-in from the beginning, and the ability of any server to granularly discriminate against any given TLD at their operator's discretion.

He doesn't. You just can't use custom clients with his server.