Separately enable/disable sign-ups for users with and without associated Stack Exchange account

[makyen]

Currently MS admins are able to completely disable/enable registration on MS. This is almost exclusively used in order to disable registration by spammers/trolls without an associated Stack Exchange account. I don't recall a time when we've had a significant number of inappropriate accounts created with associated SE accounts. There have been some, but it's far more rare than the sprees of accounts we've seen without associate SE account.

So, I'd like to see two controls similar to the single control which currently exists, but adjusted to be:

• Enable/disable registration for users without an associated Stack Overflow account
• Enable/disable registration for users with an associated Stack Overflow account

I say Stack Overflow, because what's really required is a Stack Overflow account, due to how the SE API's OAuth2 flow actually works.