I’m in same direction in my project. For now I manage folders as a content type with its own Access Control List. This ACL is a bit complex, because I have groups of users (assigned by admin), teams (assigned by users theirselves), and shared folders, all with read/write/admin rights granularity.
I don’t expect that media folders can cover or replace my needs in terms of ACL but it could be expect that basic ACL functionality will be demanded.