They will continue to use UIKit / AppKit for their own apps. They will just make it so that doing so will require a private entitlement. 3rd party apps will be

They will continue to use UIKit / AppKit for their own apps. They will just make it so that doing so will require a private entitlement. 3rd party apps will be restricted to SwiftUI. Apple is very much in the camp of maybe tolerating third parties, but only so long as they only ever do stuff in the bounds of what Apple wants them to do