Title explains all.
SE currently supports logging in with GitHub, Google and Facebook.
In terms of tracking user behavior, Apple seems to be a better login option to me than Google and Facebook.
Reverting to the concerns stated in response to the question:
What benefit it will have?
With users having an option to use a different login service than FB/Google/GitHub, I think they will be able to keep their privacy. At the very least they will be able to decouple their activity on Stack Exchange from Google and Facebook.
The feature development is going to cost time.
I can't argue against that. If there are other pressing items to work on in the pipeline, go ahead with them. However, I have worked on security and authentication myself and fairly understand the time this login option can take. Most of it is research than development. I found that after I implemented the first one, others were quicker to implement. I have never implemented Signing in with Apple, but if Single Sign-on with Google and FB is present, Apple should not be hugely different.*
Is that option going to benefit a substantial number of users?
That's better answered by people working at SE. Or those of use who have access to site's analytics, they can see how many users are accessing SE network from macOS/iOS/iPadOS. I think if properly implemented, a majority of SE users on Apple's OSes will gladly make the switch. A "proper" implementation could be along the lines:
- Allow new users to Sign in with Apple;
- Give the current users an option to move to Signing in with Apple;
- After migrating the existing users delete their older login info;
- Alternate to step - 3, have people create new account by Signing in with Apple and then merge their current account with that.
This way they retain the profile and rep but trackers can't link their activity on SE with their activity elsewhere on the web. Apple's users are generally very quick to adopt the latest. This is something that Apple proudly states in their events too.
Of course this is based on the faith that SE does a good job of deleting PII that users have provided earlier.
We had to de-ship Open ID.
Yes, in hindsight it may well turn out that Signing in with Apple was not as popular as thought. So this effort becomes a risk that doesn't pay off. I'd still say.. try it out. When this has been implemented and a blog on SE about this feature demonstrates it to users, SE will have a huge chunk of happy users.
As people are becoming more and more aware of their privacy online, when they will see an option that gives them convenience (Single signing on with Google / FB / GitHub (aka Microsoft)) and an option that gives them convenience and privacy (Single sign-on with Apple), then if they can pick the second option, they will pick it.
Even if the existing users do not migrate, the new users will use it because for them Signing in with Google or FB is exact same effort as Signing in with Apple.
Creating an account on SE sells you out to only SE.
Not true. There are multiple trackers embedded in SE pages. In fact on this very page that you are reading there is one tracker each from the following:
On a 'Hot Question' on a Stack Overflow page that I opened, apart from the three above, there were two trackers from Google.
However, it is true that to block those trackers you do not need a full-fledged Sign in with Apple. Latest Safari (v 14.0.1) blocks them today. If you're not on Safari, you can install DuckDuckGo extension on whichever browser you are using and hide your ass.
To make a stronger case of why this option is something to be taken seriously and could be well worth developers' time, this is a screenshot of the latest spam I received. The only place I have even used the word 'vacuum' is in a comment I made on this question itself. Otherwise I have no issues with my vacuum cleaners and have not spoken about them to anyone.
Because I visited this page a few times to respond to the activity on it, 'selling a vacuum cleaner' was identified to be a critical thing for me by data harvesters.
*Feel free to correct me. As I said, I have not implemented Signing in with Apple in my software.