Languages don't get open sourced - language implementations do. So a real informative article would talk about why apple would or wouldn't propose Swift to a standards body as a new language.
My understanding (from Apple employee comments, including by Chris Lattner who created Swift) is that the language is evolving in the open now. Version 1.0 is going to be supported by iOS 8 tools, but that doesn't mean there may be several updates even over the next year to fundamental language concepts. Languages evolve from use; the best way to make Swift better is to have people both inside and outside of Apple start using it and providing feedback.
They actually designed the swift implementation to make more rapid evolution of the language possible; there are no components at the OS level or shared by applications. Instead, you bundle your application and dependent libraries with the swift runtime corresponding to the compiler version used to compile every swift thing in that bundle. In exchange for more space used by duplicating libraries, they can actually let you ship and support older swift code that might not even compile with the newest tools due to language changes.
In that environment of rapid innovation, attempting to standardize the language or to promote alternate implementations would be insane. However, these are both things which I've seen hints are desired once the language calms down. If Swift is proposed as a new language to a standards body, it is incredibly likely that Apple would also give components of their Swift implementation to the LLVM project.