Again, I disabled IPv4 purely for testing reasons, to guarantee nothing was using IPv4 without me knowing it. There’s no reason to actually disable IPv4 as a fallback.

Over 99.999% of traffic through my home network is IPv6 now. The tiny remainder that has to use IPv4 does, without issue. 5 months on, and nary a complaint. Just works.

The world is ready for IPv6 as your primary, with IPv4 as the fallback.

I understand that. I'm just saying that the people who don't want to try IPv6 aren't motivated by that. For many the calculus is simply functionality divided by effort. They're not configuring IPv6 because it's hard or because it doesn't work. They're not configuring IPv6 because they already use IPv4 and it still works for them.

Not really. When I worked in a networking company, we've observed that connections between hosts via IPv6 were often worse than with IPv4. By connection, I mean between two hops on route to your destination.