Agreed.

For users using other shells, the issue is not knew.

The main recommendation I've seen (e.g. for Fish) is that the user kept a
POSIX-style shell as a login shell and only drop into the desired shell after
the profile has been loaded.  This way, Guix and similar configurations
(/etc/profile, etc.)  can be sourced properly.

See here:
https://wiki.archlinux.org/index.php/Fish#Setting_fish_as_default_shell

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