Earlier quoted context omitted.
Yes? I don't think it's a bad idea though. If only for bringing the issue to the public And while I do think an alternative would be good, the fact is that protecting the private key is the most important part (for example by keeping it on a smartcard with NFD) - hence why the need for a secure device "but I want to install alternative Android etc etc" yes that's fine - but you know this is a non-secure-(enough) env.
Physical SIM cards are just as secure as the security enclave on the phone. In Norway few years ago banks even used that for secure authentication that worked on dumb phones with local mobile network providers pre-installing the required software on their SIM cards. But then to save cost including the support cost banks stopped and instead started to require a non-rooted Android/iPhone.
But I think there are still cell operators without sim card