It totally depends, to be honest. There are countries/ ISP with a very high IPv6 adoption, but also some that don't care at all.

The idea is to use the built-in reverse proxy for proxying HTTP(S) requests and provide an IPv4 + IPv6 endpoint for your domain.

That means your end users won't even notice the server is running on IPv6 only

Google has some interesting stats on the IPv6 adoption rate: https://www.google.de/ipv6/statistics.html

Thanks for the info.

Do you know if the average person in America will be able to access an IPV6 site from a browser without a reverse proxy of any sort?

US IPv6 adoption is at 51%, so the answer is just barely yes.