From what I can see, he also readily admits that IPv4 and IPv4+ hosts cannot talk to each other, or more clearly, we cannot start using the extended address space before almost everybody has IPv4+ capable software.
I don't know whether to respond to that with "what?" or "yeah, so what?" but I'm leaning toward the former. IPv4 and IPv4+ hosts would communicate with each other, but IPv4 would only be able to communicate with the overlapping range of IPv4+.
Addresses in this range would have initially been relatively valuable but their value would be expected to decrease over time as more hosts started working over IPv4+.
I think djb was right, but obviously we're unlikely to ever find out.