Implement Apple login as registration method!! https://developer.apple.com/sign-in-with-apple/
Facebook and Google are already there, I think it would not be a big problem to add the Apple one too!
I don't think that I will add it. There's already a standard e-mail registration which doesn't depend on any 3rd-party provider so I don't see the need to add new login methods.
There are always issues with them — user's Google/FB/Twitter account could be suspended, there could be issues with API (they're rare but they exist), they could be sunset (like many OpenID services and Mozilla Persona) so I prefer to not bother with them.
Marc van Breemen commented
This idea is 2 years old. Any idea if this will be implemented?