That's quite true, but in this counterfactual, IPv4+ doesn't pretend that 6to4 is just a transition mechanism to an all-IPv6 future. That is, IPv4+ is as-if 6to4 was the default, preferred, or only mechanism, and core routers were never demanded to upgrade.

It's an edge based solution similar to NAT, but directly addressable. And given that it extends IPv4, I think it would have been much more "marketable" than IPv6 was.

But again, this is all counterfactual. The IETF standardized IPv6, and 30 years on it's still unclear that we will deprecate IPv4 anytime soon.