I know it's mixing of layers, but I can't help but feel the IPv6 transition missed the boat when they didn't just get rid of ports in the process. They've changed so much else anyway.
Want to run another webserver instance or whatever on your computer? Get the OS to allocate a new IP for it. Ports be damned.
Could be implemented in a backwards compatible way by requiring all IPv6 TCP/UDP traffic to use a fixed port number.
ipv6 packet does not have any port field. ports are on the level of tcp and udp, and you don't have to use tcp or udp on top of ipv6. ipv4 packet does not have any port information as well.
Conceptually its doable on linux and ipv6. Have the listening program sit on that default port of 80.
Something involving socat, an any-IP / TCP routing rule, a VPS or other machine with a ipv6 /64 and plenty of duct-tape.
You'd get an application sitting on port 80 accessible via some unique ipv6 address (in the /64) on a tcp port 80. They needn't be the same port number but it would make it easier.