There are a couple I have in mind. Like many techies, I am a huge fan of RSS for content distribution and XMPP for federated communication.
The really niche one I like is S-expressions as a data format and configuration in place of json, yaml, toml, etc.
I am a big fan of Plaintext formats, although I wish markdown had a few more features like tables.
The X is for extensible, so are a whole bunch of other protocols and people haven’t stopped using them, they get improved upon (for the most part).
The mentioned permanent tcp ip connection (which you don’t neccessarily have on mobile) too?
I was under the impression XEP-0060 solves that.
Sorry, i won’t read that whole thing. But i guess you’re right, in which case i take back what i said.