You just described https://github.com/sakurity/securelogin
While I congratulate you for your efforts, I can't really see the point of implementing this outside of the browser as anything more than a proof of concept. The whole idea is to replace the trust in a web service with the trust into the user agent, I would approach this as specification/standardization work, not something you whip up an electron app for.
The Failsafe work is fascinating, I just discovered it thanks to your link and I'm digging in.
It's definitely would be more successful being part of the browser, but Web Auth API is too slow to move so I went out to make a PoC instead. In the end: I hate electron apps now :) Also I now know what kind of effort is needed to change the auth space... I don't believe it will happen short term :/ It's too hard and too little incentive to change things.
The only perk of being outside the browser is being able to auth regular desktop apps like Spotify or Btc wallets. But yes, 99% are web apps so seamless in-browser login would make more sense.