[tedk-42]

I don't think this is how it would have played out at all.

I'm no expert on IPv4 or IPv6, but if they had designed IPv6 to be able to route fine to IPv4, we'd be OK.

It would at least give people an upgrade path where their old stuff that couldn't be patched / updated and were stuck on IPv4 could be slowly killed off in the path of least resistance down the dependency line.

This 'dual stack' approach doubled up on everything up front and meant we all had to do both during the transition (which has taken 30 years).

[p_l]

IPv6 explicitly supports all sorts of transitional technology, including being able to map v4 addresses to v6 that are used with translation gateways connecting from v6 to v4 (widely used in mobile networks to provide any v4 access).

That still requires that if you have used BSD Sockets before getaddrinfo was added (or like many, didn't learn about it for years) then you had to rewrite the parts of your application that are responsible for handling connections.

So the very thing you're advocating for exists