This looks fantastic!

I can see quite some overlap with Shepherd User Services:
https://lists.gnu.org/archive/html/guix-devel/2019-02/msg00128.html

What do you think?

If we implement shepherd user services, we would essentially be able to
declare most (all?) of a user home folder.

The main difference I can see with Julien's approach is that the
declarativeness is not enforced since home would not be read-only.
Home would be initialized declaratively, but then the user or any
program is able to overwrite files in home.  Which may or may not be the
desired behaviour.

Cheers!

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