Hi,
I don't see anything in the patch itself, that is specific to Guix, so
it should probably work upstream as well. This issue is likely going
to affect other functional package managers like Nix too, so it would
be nice, if we can get the patch to be accepted upstream. However, it
does add a specific exception just for fonts, while other resources are
still taken from XDG_DATA_HOME. As such, it is still rather an ad-hoc
solution to a very specific annoyance than something "general".
I'm also not quite sure, whether this could cause problems with the
number of arguments being passed to the bwrap process exceeding some
limit. It has not yet come up so far, but I thought I'd mention it.
However, if it does, we're going to be the first to notice with our
huge environment variables, so that's probably a bigger deal here than
elsewhere.