Limit User field type to specific group or user type

[spaceageliving]

I have a User field type on a collection that is used for the entry Author.

How can I limit the names in the User list (dropdown) so that it only shows specific user type(s) and/or groups(s)? I don't want to show all users in the system, only "writers" and "editors".

[jasonvarga]

You can't - aside from making a custom fieldtype - but it's a good feature request.