User, Groups or lists of either

I saw someone else asked about ForeignKey support, this might fit into that. Is there a way of adding lists of Users or lists of Groups (or, better, lists of either).

What I would like to do is have an app setting to have an ability in an app based on the user being in a 'permission' list (list of users or groups). Do you think this would be easy to add?

No files, tests, or entry points are named. Start by reviewing the existing app-setting field types and the related ForeignKey support mentioned in the issue; define the supported user/group-list behavior and a testable permission-list outcome before implementation.

Written by the indexing model from the issue text.