> We could presumably have done something like: use the IPv4 packet format, treat the 32 bit src/dst address in the header as the first 32 bits of the address and put the remaining 96 bits (+ checksums/etc.) as the first few bytes of the payload. Then create TCPv6, UDPv6, IGMPv6 etc. protocol identifiers for the protocol field to distinguish traffic that's encoding an IPv6 address in the first few bytes of the payload.

So no router can route it sensibly and no existing client works ? How would that help ?