It was relevant then -and it is relevant now- because there are good lessons in how to migrate from thing A to thing B, even if some of the then-missing necessary bits are in place now.
Still, it's almost certainly the case that DJB's rant had no real effect, and that the necessary steps were bound to be taken as the cost of sticking with IPv4 rose. Also, a significant period of time was always going to be necessary for software and tooling to catch up -- perhaps there wasn't much to be done about improving the transition 20 years ago. Yet DJB's rant isn't wrong or devoid of value -- it's mostly right and entertaining (still!), even if there just wasn't enough IETF and dev oomph to do better at the time.