Idea

What is required to get ISPs to provide IPv6?

Internet providers saying "there is no demand"?

What if sites start show warnings for missing IPv6 support?

With inspiration from browser-update.org, maybe something similar can be done to warn about lacking IPv6 support.

The banner/popup

Include the small <script async src="https://ip-update.net/ipupdate.js"></script> on your webpage and visitors without IPv6 will get a notification linking here. screenshot

Missing IPv6 support

You might have come here due to a connection test over IPv6 failing. This is an issue because some sites are IPv6 only and might not be reached over the legacy IPv4 internet.

Resources

Acknowledgements

The ip-update.net logo is based on the logo from worldipv6launch.org, used in accordance with CC 3.0 license
Inspiration from browser-update.org. Tests using ipify.org IPv6-address API.