What's the state of developing iOS apps in Linux? [closed]
There's a misunderstanding here.
Swift the programming language is open source.
It doesn't mean that iOS or OS X frameworks, like Cocoa, UIKit, etc, are available in Linux - Apple didn't announce that.
When you make an app for iOS using Swift, you have to import UIKit and other libraries - those are the iOS parts.
Swift is just the language - you can already make an iOS app with Ruby, Objective-C, JavaScript, etc, using these same libraries.