I don't know, I don't share your pessimism. In my personal experience, most hardware isn't unhackable. Apart from iPhone / iPad (where hardware and software are non-standard, and also made by the same vendor) I struggle to find any examples.

I have installed Linux many times on Chromebooks, where there is some BIOS module that checks for OS "authenticity", but that can be disabled. I have flashed ROMs on android devices many times too. It's sometimes a bit inconvenient, but nothing remotely close to impossible.