Quake3World

I dont know if this is completly true, but suposedly quake champions was first meant just as a quake live graphics update and later on decided to be made into a full game. If so, i guess that would explain why qc has a renderer that was developed by saber and not id. Another clue was syncerror talking about quake live 2.0 in a cryptic manner as if to create a hype, but this settled down after a while and no mention of ql 2.0 again.

So is this something thats possible, replacing q3 renderer with something on the level of quake champions? or are ioq3 and berserkers graphics improvments the fartherst we can push q3?

Well, once you have complete access to Quake 3's sourcecode (which we have), you can do anything you want.
Thing is, once you've got a renderer with all those features in place, that means you're gonna have to rebuild all assets as well to make use of those features.
This means you're basically building a whole new game again and having to deal with the legacy of the Quake 3 code base is just not worth recycling that. It's easier to start from scratch.