Music discussion threads don't last in the first place. People don't want to talk about music, they just want to show everyone what music they're listening to and all the bands you've never heard of.

A music subforum would be this --

Somebody posts a thread about car sick cars saying hey these guys are rad.

The following posts are:

"Cool I'll check them out."

said in four different ways. Thread is done until they release a new album.

In a way a subforum just becomes just a giant list thread. Which is what all music threads become anyway.