While the current draft is sufficiently self-consistent IMO, there is a lot of work still needed in other drafts to make "IAB treatment" references valid. It would be nice to get a nod from IAB/IESG regarding our current direction (based on the "IAB treatment" draft) before we spent time documenting specific details (e.g., OPES-Via header format for HTTP). We need to get WG consensus first, of course.
Thanks, Markus