[yellowapple]

What's the likelihood of supporting disposable 6-digit codes a la Google Authenticator or Authy? It would be kind of neat to be able to implement this sort of thing without having to request any contact info at all (sites that require phone numbers are annoying, and there's only one email-based option AFAICT); just provide a QR code and tell the user to scan it with their 2FA app of choice, or (optionally) fall back to requesting a destination for verification codes (i.e. for those who don't have smartphones but do have email addresses or SMS-capable dumphones).

[toomuchtodo]

Not every language has drop-in support for 2FA, but Python/Django has a pip package: https://pypi.python.org/pypi/django-two-factor-auth