It isn't clear what to do if a route change happens during a
Query/Response/Confirm cycle and no messaging association is being created. The
current draft would send the confirm using the flow source/destination
addresses, which would probably be seen as an error condition at the new
downstream node.

Probably, the right approach is to direct the Confirm explicitly to the
downstream peer, and rely on other mechanisms (network hints or soft-state
timeout) to pick up the routing change independently.