What I argued was that IPv4 could be embedded into IPv6 address space if they had designed for it. But I agree, that the actual packet header layouts would need to look at least a bit different.
Like:
> Addresses in this group consist of an 80-bit prefix of zeros, the next 16 bits are ones, and the remaining, least-significant 32 bits contain the IPv4 address. For example, ::ffff:192.0.2.128 represents the IPv4 address 192.0.2.128. A previous format, called "IPv4-compatible IPv6 address", was ::192.0.2.128; however, this method is deprecated.[5]
* https://en.wikipedia.org/wiki/IPv6#IPv4-mapped_IPv6_addresse...
& the following section for the follow-up embedding.
(What's up with people constantly suggesting that v6 should do things that it already does?)
The result is basically the same situation we are in today, except much more hacky. You'd still have to do a bunch of upgrades.
