Swift is a programming language. Anyone can write a different compiler for it. Open sourcing Apple's LLVM frontend would be nice, but is not required.
If it's not open sourced and no one does a Swift implementation, we'll be exactly in the same situation as before. You had to write Java for Android and Objective C for iOS. Now you'll have to write Java for Android and Swift for iOS. I fail to see how that changes anything, except Swift being slightly less annoying thatn ObjC.
90% of the article serves to show that the author doesn't understand the difference between a programming language and the libraries provided by OS X. The other 10%... well I didn't notice what it was about.
And this crap makes Slashdot...