The crazy thing? There is already two WiFi QR code standards, but they do not include the CA cert. There's a "Wi-Fi Easy Connect" standard that is intended to secure the network for an enterprise, and there's a random Java QR code library that made their own standard for just encoding an access point and WPA shared key (and Android and iOS both adopted it, so now it's a de-facto standard).
End-user security wasn't a consideration for either of them. With the former they only cared about protecting the enterprise network, and with the latter they just wanted to make it easier to get onto a non-Enterprise network. The user still has to fend for themselves once they're on the network.
They only stopped using global default passwords because people were being visibly compromised on the scale of millions at a time.
It might be easier to extend the URL format with support for certificate fingerprints. It would only require support in web browsers, which are updated much faster than operating systems. It could also be made in a backwards compatible way, for example by extending the username syntax. That way old browsers would continue to show the warning and new browsers would accept the self signed URL format in a secure way.
Now for issuing certs to devices like your router, there’s a registration process where the device generates a key and requests a cert from the CA, presenting its public key. It requests a cert with a local name like “router.local”. No cert is issued but the CA displays a message on its front panel asking if you want to associate router.local with the displayed pubkey fingerprint. Once you confirm, the device can obtain and auto renew the cert indefinitely using that same public key.
Now on your computer, you can hit local https endpoints by name and get TLS with no warnings. In an ideal world you’d get devices to adopt a little friendly UX for choosing their network name and showing the pubkey to the user, as well as discovering the CA (maybe integrate with dhcp), but to start off you’d definitely have to do some weird hacks.
It also helps that I know exactly how easy it is to build this type of infrastructure because I have built it professionally twice.