I would say this analogy is not properly when talking about IPv4 to IPv6 transition. Moving from Python 2.7 to 3 is a pure software problem while moving IPv4 to IPv6 is hardware, software, and logistics problem.

There are number of embedded OSes and devices that do not have firewalls nor the ability to disable network ports. Example of these invisible world items are motors, servos, PLCs, and label printers that get configured over IP. These devices do the bare minimum to get the IP stack up and running. These UI tools also need to be updated for allowing configuring an IPv6 address.

I would love to leave IPv4 and move fully to IPv6. Currently it is not cost effect to do so at scale. Companies do not want to spend money on the extra hardware to allow their IPv4 devices to talk IPv6 when they can save that money and keep running IPv4. Nor do they want to spend money on newer hardware. I still have clients running Windows XP Embedded, hopefully air gaped, in the automation world.

*You would be surprised on the number of large corporate IT managers that rather have a completely open label printer connected directly to their network instead of bridged behind a state full firewall running Windows or Linux hosting the main product.