> Keeping a persistent connection to your server [...] is not a simple problem

But is already solved. Explanations : "The State of Mobile XMPP in 2016" https://gultsch.de/xmpp_2016.html

> Federation has the problem of being harder to prevent abuse.

Precisely XMPP have already solutions for this problem

> And when you control the whole infrastructure, it's easier to provide a good user experience. With federation, you are depending on the quality of other's implementations.

Answers here : "Objection to ‘The ecosystem is moving’" https://gultsch.de/objection.html

You might also interest by GnuNameSystem wich is a federate, decentralize and censorship resistance DNS https://gnunet.org/gns