It would be a nice feature to be able to set some kind of email preference whenever a custom "users" field is defined within Maniphest and whenever this field is set / updated.

Example: Pretending I have a custom "reviewer" users field, where I am able to set one or more user(s) to review whatever my task may have been.

• Whenever this "reviewer" field is set with a user; this user should be notified by email that it's name has been set.

I guess the desire is somewhat to let these kind of custom fields behave as the "Assigned To" field?
(See Q187 for a relevant question in this context)