1. a tarball was removed or modified upstream

It would be great to have the ability to install the latest release in all the supported ways on all supported architectures, and have the ability do guix pull without problems.

Last time I tried that it did not worked, because one of the upstream linux-libre tarballs was removed. It would be nice if we could afford to host the sources, so that at lesat a bare-bones guixsd suffered no such problems.

2. some packages take very long time to build (notably guile)

It would be nice, if we could provide the substitutes that the current core-updates gnu-build-system needs. That would make development that needs to be done on core-updates much more pleasant to those who are working in a restricted hardware environment.  

WDYT?