Since it's all just Guile Scheme, a full programming language, you can extend it in any way you want, and use the Scheme libraries you want, doing whatever network access you please.
The builder is sandboxed, the whole model goes out the window otherwise.
Also, I really doubt Guix moves the needle much here. It can't make Julia magically more reproducible without effectively doing the same techniques you'd have to use in Nix.
Also, I really doubt Guix moves the needle much here. It can't make Julia magically more reproducible without effectively doing the same techniques you'd have to use in Nix.