Yep, we have integrations for many services, but software must integrate or support SAML (as Github Business/Enterprise does) for us to do 2FA. Our core product isn't really 2FA however, and we have different target markets: Duo primarily targets businesses looking to protect the services their employees access, while it sounds like you're trying to provide better UX for any consumers of 2FA.

I completely understand your approach and think it's a really neat idea. Looking forward to seeing it. :) Feel free to connect with me via email, I'd love to beta your product.