For you information there is a new draft being considered right now at the IETF group called The ORIGIN HTTP/2 Frame which (once approved) will allow a boost in performance when using connection coalescence to a given origin (the draft is co-authored by Akamai's Erik Nygren)
The HTTP/2 specification (RFC7540) allows clients to coalesce different origins (RFC6454) onto the same connection when certain conditions are met. However, a 421 status code is returned when a connection is not usable for a coalesced origin. Using a status code in this manner allows clients to recover from misdirected requests, with the drawback of adding latency. To address that, this specification defines a new HTTP/2 frame type, "ORIGIN", which allows servers to indicate what origins a connection is usable for.