If it's going in the same spot in the packet header as the current IPv4 address, how do you make sure that the 20-30 routers owned by 3 different companies that are likely to be between your computer and the destination computer exhibit a behavior that is consistent with moving packet closer to the destination?
(If they don't, you've just made a version of IPv6 that is worse-- it's missing the last 30 years of IPv6 implementation.)
It's written above, bridge destination address in the "legacy" IPv4 destination header, and that bridge can be figured out by looking up the reverse dns entries on a IPv4 Extended IP, until the user is natively using an IPv4 Extended network.
This brings the packet closer to the destination.
The new address goes into the Options field, you can store lot of data there (somewhere up-to-60 bytes, and we need 1 or 2 byte actually).
Reminder: The goal is to add one-byte to have more IP addresses, not rewrite the whole internet.
Here it looks like the guys wanted to fix that IP allocation problem, and then they went all-in, and decided to rewrite everything at the same time.
It's ok, and even a good idea in theory, but network administrators don't like to be pressured "in emergency" into upgrading to this solution.
The practice shows that people rather prefer doing NAT than IPv6.
https://datatracker.ietf.org/doc/html/rfc791#page-11
Where is that new address going in the header?
If it's going in the same spot in the packet header as the current IPv4 address, how do you make sure that the 20-30 routers owned by 3 different companies that are likely to be between your computer and the destination computer exhibit a behavior that is consistent with moving packet closer to the destination?
(If they don't, you've just made a version of IPv6 that is worse-- it's missing the last 30 years of IPv6 implementation.)