There used to be a form response people would post in discussions about ending spam or similar. Something like Your proposed anti-spam measure wouldn't work

There used to be a form response people would post in discussions about ending spam or similar. Something like Your proposed anti-spam measure wouldn't work because - [ ] it assumes mail administrators operate in good faith - [X] it assumes all systems can be upgraded in a timely manner - [ ] ... We could probably have the same for IPv6. The proposed method - [ ] for an alternative to IPv6 - [X] to avoid the transition to IPv6 - [ ] to allow us to keep using IPv4 indefinitely would not work because - [X] it would require replacing all the hardware and updating operating systems anyway - [ ] it does not expand the address space to the extent required - [ ] etc.