As soon as we get to about 70%, I reckon some games and apps will stop supporting ipv4 on the basis that nat traversal is a pain and dual stack networking is a pain.

If you spend 2 days vibe coding some chat app and then you have to spend 2 further days debugging why file sharing doesn't work for ipv4 users behind nat, you might just say it isn't supported for people whose ISP's use 'older technology'.

After that, I reckon the transition will speed up a lot.