I'd argue the future isn't just federation but bridging. We have already seen repeated attempts on the client side to abstract IM platform - Pidgin being the largest, but a ton of effort was invested into the Telepathy framework for about a decade.
The adoption rates show a general failure of the model.
Server-side transparent interoperability like Riot has with several services, however, seems extremely promising as a way to break that cycle.
XMPP was a tower built too tall and wide and it crumbled under its own optiomal extension weight.
Just bridges mean you are still selling your soul to a primary operator, which prevents trust.
Federation and bridges without extension hell means you can use whatever homeserver you want, bridge to whatever you need to, and finally have working interoperable IM.
The adoption rates show a general failure of the model.
Server-side transparent interoperability like Riot has with several services, however, seems extremely promising as a way to break that cycle.