The 2 largest ISPs in my area (and 2 of the largest in the US), AT&T and Comcast, both support IPv6.
You might be surprised. Almost every cable company in the US does, so most Internet users in the US could have ipv6.
The problem is usually the $50 wireless access point most people bought 5 years ago doesn't pass ipv6 through.
Spectrum (formerly TWC) in Dallas does not. I still run an he.net tunnel on my router.
Last time I checked (a few months ago), UVerse in Dallas didn't either.
I wonder if it's a regional thing? A friend of mine has spectrum from Charter (formerly Bresnan in this case) and he gets ipv6.
Spectrum/TWC has had IPv6 via DHCPv6 with prefix delegation for a few years in Louisville, but only with a select set of modems. A Juniper DOCSIS 3 wouldn't work for me while a Motorola had no trouble.
I had IPv6 from TWC, then for a month or so before the merger it went MIA, and then about a month after the merger it was back. For some reason I get a more reliable path to my IPv6 gateway than IPv4, so I missed it quite a bit.
Servers in different regions don't have to do double nat. You may not have this problem, but some people do. And it sucks.
Sure, if by most you ignore Comcast, Time Warner, Cox, T-Mobile, Qwest, Charter, Verizon....