Hello Mark:
Any such "transition plan" whether "working" or "straightforward" is logically impossible. Why anyone thinks such a mythical plan might yet be formulated some 20+ years after deploying any of ipv6, ipv4++ or ipv6-lite is absurd.
This is dishonest, considering that I just proved on this very thread that such ideas existed and were published. Unless you prove me that the method I pointed at does not work. It was published exactly 20+ years ago. It does both the tricks of maintaining the IPv4 Internet as is and stateless IPversion translation for smooth transition. I've seen multiple other variations of using IP in IP at the time; none of these ideas emerged, proving more of a lack of desire than a lack of existence.
The logic goes: we support legacy "do nothing" ipv4 deployments forever. We also expect those same deployments to invest significant effort, cost and risk to move off their perfectly functioning network for no self-serving benefit.
There be unicorns and denial of human nature.
There is tussle in the real world, as so well explained in a David Clark's paper already linked in this thread. The technology evolution tussle could be the next section in the paper. Those who desire it, like Africa for lack IP addresses or like Operational Technology for lack of capabilities, vs. those who face a cost and no benefit, IOW, as you say, human nature, with those in need vs. those in a comfort zone. Like the paper says, the tussles in the internet reflect the real world. I see that tussle, rather than the tech or the claimed lack thereof, as a major reason for the stagnation, rather than the lack of capabilities to adapt the technologies, be it v4 or v6. But putting that blame on the technology lacks honesty. Another example: SLAAC (to Eduard's point today on this same thread). I agree that SLAAC is an unfortunate design with the eyes of 2020. But Address Auto Configuration was redesigned 10+ years ago to enable a deterministic knowledge by the network and provide equivalent to better control than DHCP. This would serve the needs that I have seen on this list. My view is that, if there was a desire to deploy any of that it would be done. Keep safe; Pascal