> Crucially though, if we change it, we just have to change how addresses are allocated, not change the protocol again.

Yup, and only less than an eighth of the total IPv6 address space has been allocated [0] [1], so there's still plenty of room to expand, even if we have to throw every current address out and start from scratch.

[0]: https://www.iana.org/assignments/ipv6-address-space/ipv6-add...

[1]: https://datatracker.ietf.org/doc/html/rfc3513#section-4