I love the concept of this, but I'm out of the use case for the time being (Windows / Linux user). The other key annoyance is that none of my desktop computers have bluetooth, because I built them for gaming, not wireless peripherals.

That being said, you probably already thought about using a centralized server or other methods of communication. Either it'll kill battery, or require some intermediary server - which would probably need two-factor authentication to authenticate.

Though, overall, I love this idea a lot more than backing up my Google Authenticator app with Titanium Backup and restoring it each time I change phones/ROMs.