Group Membership Search results limited (per attributes on the group, or parent stems)

I have often wanted to restrict users from being able to select subjects to a sub set of the Subject ID's. ( Think "Only Employees", or "Only Employees in Department x".)

While there are "require" capabilities, it does not restrict the user from trying to add "invalid users". I think it would be better if the user's search members could also be restricted based on meta data on the group (or it's parent stems) such that the Subject search could be restricted to a combination of:

    A single Subject source

and/or 

    A single Grouper Group's current memberships

I picture an attribute def  "GrouperMembershipSearchDef".(Single assigned to groups/folders) with two AttributeNames: "SearchSubjectSource", and "SearchGroupMembers".

SearchGroupMembers values could be full path names for groups, ( preferred ) or their groupIDs ( much more compact, but very hard to decipher for a human. )

If you want to be even better... let the attrDef be multi valued and support N Subject Sources and N SerachGroupMembers values in the search.