https://issues.guix.gnu.org/39728

I contemplated another way to improve on download speeds, by spawning a
single ‘guix substitute’ process and thus potentially reusing
connections, but it’s trickier than it seems.

Can I help testing this patch?

PS to yarnton: Note that Nix would also have to catch up on some
features: grafts, authenticated checkouts, reduced binary seeds, etc.
;-)

I know! That's why I'm trying to migrate to GuixSD. And I say this as a maintainer of a dozen packages in NixPkgs.

Another big motivation is that Guix packages are cleaner and well tested. Nix has quite a few things that are half broken. I've fixed some that I use myself, but it's too much work to get it all sorted.