> I like that Facebook is now a glorified version of OAuth

I don't. One company should not have the power to decide whether I should be recognised as a legitimate individual or not, and they should not act as a gatekeeper between me and my online identity. I don't care how benevolent that one company genuinely is.

If an intermediary is necessary (like an email provider for mere mortals), I should be able to choose a service provider.

If you go here https://www.facebook.com/settings?tab=applications you can see all your logins. You can migrate each login, one by one, using an app like 1Password to generate new passwords that you don't have to remember.

Some services/apps may be able to transfer stuff to a new account. When I deactivated my Facebook account, I had Spotify linked to it. I created a new Spotify account with an email and contacted their support to transfer everything to the new account and deactivate the old one, it was quick and worked flawlessly.