> 3. Forget about crazy site which by someone's folly only have IPv6 address.
Folly? You mean the address exhaustion. Yeah, let's do that. That'll work as well as the current plan. Which is to say not work at all.
> either you have IPv6-capable OS
I have an IPv6 capable OS. I have a relatively new DSL router with very young software on it. I have a valid net address. I have my DNS configured. I have my firewall configured. I've been connected to the net for a few years now using the same address. And yet, I cannot ping ipv6.google.com. That is what common sense people call "interoperability failure." I'm sure you'll have some funny explanation for this, full of acronyms like ASIC, FPGA etc. :-)