Regarding propagated inputs:

> +    (propagated-inputs
> +     `(("gsettings-desktop-schemas" ,gsettings-desktop-schemas)
> +       ("gobject-introspection" ,gobject-introspection)
> +       ("duplicity" ,duplicity)
> +       ("python" ,python2-minimal)
> +       ("python-pygobject" ,python2-pygobject)))

Could you add a comment explaining why all this needs to be propagated?
If there’s a way to avoid it, it’s even better (for instance, if
deja-dup execs duplicity, we could hard-code the absolute file name of
duplicity.)

TIA!

Ludo’.