Don't know why you're getting down voted, sure Swift has some neat features, but if any other company released something like this that was closed source, no one would really care.
C# is hideous to get running consistently (if at all) with recent versions and libraries cross platform. Perhaps this will change in the future, but they've not been particularly brilliant about it over the past decade
I don't know what libraries you talking about but nearly everything from nuget starting with image processing and ending with orms and crypto work just fine on linux.
Even more when K will come out I don't think there will be any worries at all.
He's getting down voted because his assertion that the attention paid to Swift is driven entirely by hipsterism is Slashdot-esque nonsense. People who make a living writing Objective-C will be making a living writing Swift.
no one cared if Javascript the language was open source when it was the only way to do client side scripting for web pages.
similarly Swift has iOS and OSX - other languages are available on these but I guess developers are anticipating Apple emphasising Swift over Objective-C going forward