I dont think you'd really have to host all the music, although I agree
it would be nice.
I do my advocacy bit here :
http://www.em411.com It's a really nice site
and great community - they even put up with linux nutters there :)
Anyway, they don't host the members music, just provide a way to let
people know you have releases availible, and allow people to comment on
them. It works well. They also do remix competitions, latest software
announcements (I put the last ssm release there :) ) and general forum
banter.
If a specific linux based musician's site was set up, I'd contribute,
definately - but I also think it's good to mix with people who write
music on other OS'es too - it can be enlightening to compare the
differences (it's not all easier on windows/mac these days)
dave