"In effect, it would downgrade IPv6 into IPv4+, with the plus simply being more addresses."
Good. I'm not an expert in any way on IPv6, but I know when something has been designed by a committee and IPv6 was. A spec comes in for a greyhound, and out comes a camel. IPv6 is a camel.
If they'd left it to engineers to sort out then we would have simply tacked on a most significant byte to the IP and subnet octets and be fucking done with it.