There's one of these posts in literally every IPv6 thread. > Complete backwards compatibility > If it's 8 bytes then it's a full address Existing IPv4 device

There's one of these posts in literally every IPv6 thread. > Complete backwards compatibility > If it's 8 bytes then it's a full address Existing IPv4 devices wouldn't be able tell that it's 8 bytes, and wouldn't be able to make heads or tails of such a packet. At best, they discard the packet, at worse, they misinterpret it. It's not backwards compatible. You can attempt to construe the bits however you like, but you're going to butt up against the pigeon-hole principle here. Any solution that works is going to be materially the same as IPv6.