How do you expect compatibility with v4 protocols/software/hardware/routers/ISPs to work without using v4?

That's a serious question. Do you have a way for this to work? Because I don't think it's possible (for fundamental reasons: https://en.wikipedia.org/wiki/Pigeonhole_principle), and it would be extremely unfair to criticize the designers of v6 for not fixing an unfixable problem.