Two things:

It works.

It's wonderful.

I love this. I'm logged in to Swarmops (my current project) before my phone has even confirmed it has transmitted the signed nonce. This is as smooth as Lastpass' autologins, except 2FA since it combines what you have with what you know (your phone's password, in this case).

If anybody wants to copy my C#/Asp.Net code, feel free. The relevant parts are easy to extract from Login and BitId here:
https://github.com/Swarmops/Swarmops/tree/master/Site5/Security

They may still be a little unstable with regards to threading on Mono (which sometimes cuts a request short and strange things like that), but the code works at a prototype level.

Cheers,
Rick