> You could say that ipv5 is kinda like if you made v4-mapped-v6 the only way to use ipv6, didn't do NAT64, and then expanded those to >4 bytes at a later time.

I guess I don't understand. This seems to boil down to: expand the address space, but don't actually use the additional space until a flag day that occurs after every piece of networking equipment on the Internet gets upgraded? Surely there would be even _less_ incentive to upgrade, because instead of getting local benefits that are incomplete until the entire network upgrades, you get _no_ benefits until the entire network upgrades.

This seems strictly worse than the situation we have now, where at least locally, you can reap benefits from IPv6's expanded address space. I benefit from having a routable /56 at home, even though I can't get to it from some legacy networks.