That's why I'm saying maybe set the sub-forum up there at Arch.
We would then lose the knowledge accumulated here, which would be a bigger loss. Most of the audio stuff is not particularly specific to arch (plugins, applications etc...)
But I just had a look at the arch forums and it's indeed a desert when it comes to pro-audio. People ask questions there and end up here
The typical paths seems to be: arch wiki -> arch forums -> LM forums.
It would then probably save time for everybody to simply put a reference to the LM forums on the pro-audio page of the arch wiki.
As for the content that is both arch linux & audio specific, ie anything that could justify a sub forum here, I can't actually think of much at the moment except user support.
Packaging (pkgbuild dev) questions will be best be answered on the arch forums, system tuning is not particularly distribution specific.
The only thing that stands out is arch users are often the first ones to report new bugs since they live on the bleeding edge (as already mentioned earlier).
In comparison gentoo/funtoo and other rolling release distro users seem to be less numerous or less vocal.