I suspect the big reason it hasn't happened yet is it would require ISPs to replace tens of thousands of dollars of hardware and it would increase support requests in the short term ("site XYZ is broken but it's fixed when I turn of IPv6").

That, and—unlike TLS—there isn't any class of business-destroying vulnerability whose easy solution is IPv6.

Is the hardware you're talking about the network equipment controlled by the ISP, or the routers and modems in customers' homes? I'd be surprised if the former hadn't been IPv6-ready for many years now, but I can imagine many customers are still using ancient hardware left over from when they first signed up for service.

If you have cable, a number of providers have been making customers upgrade to the newest modem. A single old modem that doesn't support docsis 3 will slow down everyone in your neighborhood.

Really? Interesting... can you elaborate/provide some reading?

I'm a software engineer with a smidge of basic networking experience so not completely clueless, but definitely inexperienced with DOCSIS and this sort of residential networking stuff.

ISPs love IPv6 because they lack IPv4 addresses.

Here in Germany, you no longer get IPv4 addresses from Unitymedia.

How to people get to IPv4 sites? Do they setup a transparent tunnel of some kind?

Yes, they use something called DS-Lite were IPv4 gets CGNATed (many customers share one IPv4).

For real. I've seen it more these days. A friend in a po-dunk town in Northern California I visited had IPv6 from Comcast. I was kinda shocked since my fiber Gigabit ISP in Seattle didn't have IPv6 rolled out to residential customers yet.

It seems more important than ever to roll out IPv6, since, at some point, IPv4 is going to become incredibly scares. Imagine a permanent/reserved IPv4 address on DigitalOcean/AWS/Vultr going from the few dollars a month to $70/month or $100/month. Forget network neutrality, regular people won't even be able to host their own content in a way everyone else can reach.

It's already a bit of a pain, as at a dollar or a few dollars a month it's approaching or over the cost of some servers I want to run.

But I expect things will continue slowly being replaced, as more switch over the stress on IPV4 lowers.

There's a real and immediate value for users if HTTPS is used. I don't see the immediate value for end users when IPv6 is used. Worst case, the lack of NATs makes tracking easier.

IPv6 is certainly necessary but nothing users have to worry about.

Https has googles bully pulpit behind it and even though https has its issues it pales into insignificance compared to ipv6's "problematic" design choices