Apple SDKs concurrency-readiness

I've been trying to use the Xcode 14 beta and the -warn-concurrency flag to make some of our library code concurrency-safe, and I've hit just… too many problems to manage.

A smattering of random data points:

• Foundation types that I think should be Sendable, are not:
  • URL
  • Notification
  • ...
• UIKit constants that should not be @MainActor, are:
  • UIApplication.willEnterForegroundNotification (it's just a string constant, and NotificationCenter itself is thread-safe)
• UIKit types and methods that I think should not be @MainActor, are:
  • UIDevice, or at least I should be able to do UIDevice.current.systemVersion from any actor
• Dispatch is completely concurrency-unaware — I kinda expected it to be unavailable, but instead it's available but doesn't understand swift concurrency
  • It'd at least be nice if DispatchQueue.main.[a]sync understood that its closure can be @MainActor (perhaps main could return a subclass of DispatchQueue with stronger guarantees?)
• SwiftUI Button etc. callbacks aren't marked @MainActor, even though (AFAIK) they are — certainly it's always been legal to update @State vars from them — so it's not legal to call UIKit from them (eg. to present a UIViewController in response to a button press)

When can we expect Apple's SDKs to actually be usable with concurrency checking?