this is exactly the sort of thought process that leads to terrible login flows. yes, it's technically possible, and it works for you.

but the login flow is one area of your product that needs to work for everybody. There's plenty of features that can be tailored to a power-user workflow because they're the only people that will see it, but the sign-in flow is not one of those. any confusing UI in your sign-in flow is going to confuse your least-confident users. and asking people using Facebook Sign-in to enter a password when they haven't ever set a password for your site is extremely confusing. all just to save a couple keystrokes for the most-technically-competent users.

I could see a lot of large companies that integrate with other B2B sites recoil in horror with a UI that encourages employees to enter their corporate email address and a password. Many employees would use their corporate passwords.