[Dagger2]

I intended the quoted part to mean something like "they did consider adding extra octets to v4 addresses and setting those octets to zero to mean v4".

It's not like they weren't able to come up with that idea. It's just that if you follow that train of thought through to its conclusion, you'll either decide it can't work or you'll make enough changes to end up with something that works basically the same way v6 does.

But yes, having enough IPs for everything was obviously a design goal. It would be excessively silly to go through all the work to increase the address size and not increase it by enough to handle whatever people ended up wanting to do with it.