https://www.google.com/intl/en/ipv6/statistics.html 45% (and growing) of all traffic to Google is IPv6. Hardly "floundered". It's just that most major ISPs in the developed world have so many IPv4 addresses they don't care that much about IPv6 yet.
Now, try starting a new ISP without CGNAT (which will lead to a garbage experience for everyone) or IPv6. You'll have to spend literal tens (if not hundreds) of millions just on IP addresses alone.
20 years ago DJB called it [0]. The same problems exist. The only place IPv6 has gained any success is in the mobile market since handsets tend to be homogeneous and therefore configurable, which does allow a decrease in load of CGNAT for carriers. However, this success is not replicated in the broadband realm and probably never will be for all same reasons outlined by DJB. IPv6 is a second class network.
Except it is not. Where it works, it works extremely well. IPv6 connections are, by default, always preferred on all modern operating systems.
I’d also take the entire article with a grain of salt, because it calls a fundamental impossibility (lack if interoperability of v6 and v4 addresses) as a “mistake”. Not having interoperability was the only way, not a “mistake”.
Virtually all the pain points have been dealt with. Any further transition to IPv6 is going to happen without anyone really noticing. Except for the couple of gamers and sysadmins who were wrongly advised to "disable IPv6" to fix "connectivity problems".
Now, try starting a new ISP without CGNAT (which will lead to a garbage experience for everyone) or IPv6. You'll have to spend literal tens (if not hundreds) of millions just on IP addresses alone.