I agree in general, but 20 years ago, people were using email to actually talk to each other. There are problems with the protocol, but those aren't related to the way it is federated imo. The reason people stopped using email to talk to each other was because the features of newer options were better -- things like IMs and Skype, which have continued to evolve into stuff like WhatsApp or whatever people use now. But, unlike email that was devised in an era when things were still being driven largely by the education sector etc, all these other solutions were made by post-dotcom era profit-driven companies.

So I agree that email has lots of problems, and some of those are certainly related to its federation (e.g., the protocol has not really been able to advance in significant ways since making changes to it is nearly impossible). But I still think it's the best example of a federated messaging protocol we have today.

Anyway that's all a bit afield, as you said. I think the bottom line for me is that whichever protocol it is, if one of these current attempts at federation is going to meet my goals, then eventually there should be a large number of commercial entities participating. I know that's not everyone's goal though, but there's a reason I don't use IRC for example.