Hi Michael,

Indeed, in practice it's not easy to tell Guix "build a system without
sound" or things like that.

An option would be to implement a feature à-la USE flags (as in Portage
on Gentoo).
This was discussed previously here:

https://lists.gnu.org/archive/html/guix-devel/2019-05/msg00285.html

I'm planning to work on it in the coming weeks.  Feedback welcome!
Stay tuned!

-- 
Pierre Neidhardt
https://ambrevar.xyz/