Quake's source code is very hackable. I forked ioquake3 for a personal project and it was surprisingly easy to add WebRTC support to the C codebase, so you could play it in your browser over WebRTC :)
If you are ever interested in getting back into the space you should come join us working on Pion (A Pure Go implementation of WebRTC). I would love to hear about what else you did! [0] I am just really trying to build a intellectually curious/supportive community of RTC. Right now everything is so anemic community wise.
I read some people tried to use it for multiplayer, but the performance suffered with more than 10 players.
You don't happen to have some ping comparisons betwen WebRTC and WebSockets?
I had the impression UDP would lower the average ping, because you wouldn't have to wait on lost packages like with TCP.