Or do the problems you mentioned preclude you from being able to do it even if you were so motivated?

I guess it'd be possible to stick with GCC 2 and just update the rest of userland: you wouldn't get glibc 2.3 but you'd get 2.2, and everything else probably still compiles with GCC 2. With a bit of care this could even be done without breaking all third-party userland software: it doesn't bother me whether the backwards compatibility stuff in glibc is bloaty or not, because the player is statically linked with (potentially) entirely its own build of glibc.

What exactly are you hoping for from a new userland?

Peter