It is a lot bigger now. I wonder how much IPv6 growth is net new hardware vs replacing old hardware

Easy, India vs USA stats show that. India had an internet boom after exhaustion so its adoption is new hardware. USA's boom predates IPv6 so its mostly replaced.

India's visible adoption stats are over-represented by lte deployment. Lots of broadband providers still don't have ipv6 and some major ones deployed it very recently.

Lots of IPv6 growth is by new ISPs that don't have the IPv4 resources that legacy ISPs have, like Reliance Jio in India.

Yep. Think about how long it took to get the whole country on dialup / ADSL, but how long it’s taking the whole country on FTTP (fibre to the premises). It’s a similar issue, as it’s not just a software upgrade, it’s a hardware upgrade as well.

How often were people upgrading computers in the 1990s and 2000s? How often are people upgrading now?

For a lot of folks when they get to good enough they stop. Understandable.

But the "good enough" of IPv4 has taken a lot of effort in the last few years. How much gnashing of teeth has NAT caused and having to invent TURN and STUN and a bunch of others things?

Anyone remember Skype supernodes?

With IPv6 you "just" have to do firewall hole punching without all the drama of packet tuple munging.

And good luck with double-(CG-)NAT hole punching.

What does one have to do with the other?