Secure individual sites

Today any user who has access to the REST Manager can create and edit new sites. At my team we're working with different sites, and it would be great to see the posibility to secure individual sites. Lets say two users (User 1 and user 2) have access the the REST Manager and there are three sites (Site A, B, C). User 1 should be able to configure site A and B, but not C. User 2 should be able to configure site B and C, but not A.

The suggested solution from Latitute is to have separate instances containg the sites, it would be easier to maintain one instance with different permissions.