It's self-hostable, and they seem to be switching to webrtc-rs, not sure whether with P2P or not:
https://trello.com/c/Ay6KdiOV/1-voice-overhaul-and-video-calling
In 2022, they claimed it was using minimal resources on the server:
https://developers.revolt.chat/faq/monetisation
They also don't seem to consider federation as a priority, but then again neither does Discord.