Pierre Kim is a security researcher who publishes vulnerability findings on routers, fiber network equipment, and ISP devices.
HN commenters cite it for its GPON FTTH insecurity research, using it to show that ISP-provided fiber equipment can have weak authentication and weak secrets.
Regardless of monentary charges (and I'm very aware of them, APNIC is even considering grants to help in IPv6 because it's in limbo for so long), even if we activate IPv6 synchronously there's still many, many problems with it, even when you permanently dual-stack it.
One is connectivity. Even theoretically we should have the same network connectivity (so to speak), you can feel the pettiness when Hurricane-Electric and Cogent fought exclusively on IPv6 (https://www.theregister.com/2018/08/28/ipv6_peering_squabbles/) I can't believe I'm saying this, but IPv6 isn't free (or at least costs the same as IPv4).
Second is security. Yes, the world is no longer scannable, but consumer routers are a dud when it comes to IPv6 security. This router (https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html) has serious problems at IPv6 security, and because it's suffix is always at ::0000:0000:0000:0001 and you've eliminate around 18 bits more because of how networks are laid, you've got yourself an IPv6 botnet, which speaking by, how do you block them? A /64 would be a good start, but OVH provides a single address per server (https://www.ovhcloud.com/vps/compare/). That's it. Don't forget that fiasco with MAC addresses (https://datatracker.ietf.org/doc/html/rfc8981), but at least that's solved.
Third, IPv6 should just work as you said. I wish that's true, but embedded devices will trip you up badly. Some don't fallback to IPv4 and instead try and try again…
Usually yes, but it depends:
https://pierrekim.github.io/blog/2016-11-01-gpon-ftth-networks-insecurity.html
Also the authentication might rely on weak secrets. I know my ISP provided FTTH router has a six letter password and a guessable username (derived from my last name), and I can't change either.
Though the research is quite old now. Couldn't find anything recent specifically for DT.