So as I already wrote, 15 years from now it may not be possible to buy something using Bitcoin without trusting some CA, which are controlled by government.
This just isn't how it works. You keep repeating this, but it's nonsensical.
You can transmit a payment request via whatever channel you want. If the x.509 non-repudiation signature in it is not secure you're still secured by whatever channel you're transmitting the data over. If you have no secure channel at all, your problem is ... kinda out of scope for the payment requests.
What would you have the payment protocol do instead? All you've done so far is list completely inapplicable things that demonstrate that you don't understand what it does at all.