Thanks for the clarification. I was mainly thinking of server-side! :-) On the client side there are apparently some subtleties about the DNS interaction if yo

Thanks for the clarification. I was mainly thinking of server-side! :-) On the client side there are apparently some subtleties about the DNS interaction if you want to literally have IPv6-only on the clients (as opposed to IPv4 CGN). If the clients do anything to not trust their ISP's view of DNS (like DNSSEC enforcement, or using DoH and an outside resolver), the ISP can't fool them into thinking that they should connect to an IPv6 address for a service that, from the point of view of the Internet as a whole, is actually IPv4-only.