I would not buy a FIDO2 token if it allowed anybody to reprogram it, including me. If you managed to make selling me such a device illegal, then may a pox descend on your house.

What about a pacemaker? Or a car?

Well, your opinion is literally illegal.

You're legally (and technically) prohibited from re-programming GPS modules, GSM modules, and probably many stuff in cars as well.

(Actually, maybe contractually when it comes to GPS modules.)

Agreed, even if solely for sustainability purposes in reducing ewaste

I agree, with maybe minor exceptions. It's probably reasonable that radio hardware can't trivially be reprogrammed to exceed regulated power limits. Or for stuff that is extremely safety critical like pacemakers (though I think for those things it should be mandatory to share source code).

Perfect. Go take your enthusiasm to John Deere, and the Xbox division.