The larger point here is that there's no benefit to the user if the experience is replacing “Login with Google” with “Login with <large exchange>”, which is what it would be for the vast majority of users. If it's saying “Login with your private key”, it would be important to think about why OpenID/Persona didn't catch on or the already-supported x509 key support which has been available for decades.
Why did SIM chips take off? Why did credit cards with smart chips take off? These both embed private keys. Even desktop computers are now embedding private keys in their motherboards.
Clearly, something is missing from your analysis.
- for one-off payments it doesn't matter anyway, you just start using the new card and that's it
- and for recurring payments all businesses already need to allow for updating your credit card details because credit cards regularly expire anyway, so having to possibly manually update all your recurring payments might be a bit tedious and annoying, but it's certainly no impossible, out-of-the-ordinary task
And yet you are unable to say what or offer relevant examples. Do you login in to websites using the key on your phone's SIM or your credit card? Both of those are amusing because they're bot not only irrelevant to the scenario in question but also something people use because that's what they were given, not something they sought out.
> what part of that says “here's a benefit to you which is worth paying $$$ for!” to a normal person?
You get to keep your contacts even if you get booted off the platform (or your contacts do).
And it doesn't cost anything.
I thought, this is one of the main points we want to avoid here, so why are you phrasing it as something so unimportant?