Per-site Designer Access

I heard of this feature coming this year but cannot seem to find where that was discussed or when exactly it might happen. Is anyone able to point me in the direction of when we might get this capability. (It has come up in many client conversations at this point.)

Per-site Designer Access - The ability to give someone (potentially a client) the ability to have designer level access to a site without giving them access to all the sites in my workspace or having to break there site off into another workspace (thus paying for multiple workspaces).