[throw0101d]

> […] and write the standard such that all valid IPv4 addresses are also valid IPv6 addresses?

You mean RFC 4291's ::ffff:0:0/96?

* https://www.rfc-editor.org/rfc/rfc4291.html#section-2.5.5

* https://www.iana.org/assignments/iana-ipv6-special-registry/...

* https://en.wikipedia.org/wiki/Reserved_IP_addresses#IPv6