BGPv5

Has anyone been involved with the IETF on submitting information on BGP-5? I am trying to understand how congestion control would be best handled. Would it be possible to add something additional in the OPEN message rather than just having MP_NLRI_REACH and MP_NLRI_UNREACH or better yet run them in parallel. If we replace the encoding of the NLRI and then withdraw the routes with these 2 attributes wouldn't that make it work? Thanks John