One idea I toyed with is automatic translation of service types from
System to Home.  The service itself would look like this:

--8<---------------cut here---------------start------------->8---
(define-module (gnu home services syncthing)
  #:use-module (gnu home services)
  #:use-module (gnu services syncthing)
  #:export (home-syncthing-service-type)
  #:re-export (syncthing-configuration
               syncthing-configuration?))

(define home-syncthing-service-type
  (system-service-type->home-service-type syncthing-service-type))
--8<---------------cut here---------------end--------------->8---

The code to do that is attached below.  The key here is that we’d define
mappings, like:

  (define-service-type-mapping
    shepherd-root-service-type => home-shepherd-service-type)

The rest of the service type graph would be automatically constructed
from this.

I feel like it would be worth pursuing this path so that there’s as
little duplication as possible between Home and System.

OTOH, it doesn’t take care of things like #:user in
‘make-forkexec-constructor’ calls and the like.

Thoughts?

Ludo’.