Thank you so much for this, Julien!

There was a thread on this topic on the mailing list:
https://lists.gnu.org/archive/html/guix-devel/2019-11/msg00002.html
(could not find the first email :p).

There were a couple other issues that were mentioned there.
This patch would be a first step towards more parallelization!

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