The important thing is not the language but the IDE and API on which the Apps is based on. Before .NET, Microsoft had no unified and modern IDE, .NET was a created in reaction of Objective-C and Xcode IDE. Because .NET was rushed Microsoft has screwed their first 4 versions of .NET, making every iteration of .NET binary incompatible with each other, forcing every Windows users to keeps multiple version of .NET runtime environment up to date. Still today many own Microsoft apps bundled with Windows are not ported to .NET, because Apps based on win32.dll runtime API needs rewrite to be ported on .NET.
Beside, while you can target other platform with C# and third party API (Mono), same applies to Objective-C and since Swift is part of LLVM and CLANG, it will surely be available in open source like everything else. How do you thing Apple is porting Safari and iTunes to windows, did you know before being OSX, OpenStep was NeXT Step runtime environment for running NeXT apps within Windows and Apple still use it for their own Windows apps?
I agree, there is nothing unique with the Swift language itself, but the revolution is with Xcode playground. Have you see how powerful it is to have a language that can be both compiled and interpreted? You can see actual result while you are coding, you've got an interactive playground and debugging tools nowhere seen elsewhere for a compiled runtime. All C derivatives languages are burden by C legacy, things like semicolon at each line was mandatory because of the teletype origine of C. It was really time for someone to rethink and bring a fresh start to modern programming language and development tools.
I recommend you to watch the WWDC 2014 Platforms State of the Union video, they show Xcode playground more in depth with interactive documentations, live results and visual debugger.
.NET was not a reaction to Objective-C or XCode - .NET was first introduced back in 2000 - long before Apple was of any real significance. To even suggest such a thing is out and out ridiculous. .NET was more a reaction to Java and the need to play better with the web. The is fact, .NET probably would not exist at all if it weren't for Sun's lawsuit... .NET was not rushed - it has naturally evolved over the last 14 years, as has every language and platform in existence.
Your comments on binary compatibility are equally absurd. The reason for multiple runtimes is for side-by-side install. It's a very practical solution to the dll hell problem that used to plague windows development in the bad old days of COM. It keeps newer applications form breaking older applications. Further, it allows newer applications to use components that were compiled against older versions of the runtime... You understand that you can use win32 components from .NET and vice versa right? Why would you rewrite an existing code base? That doesn't make a lot of economic sense. That's why you can mix in match with .NET. It allows you to extend your legacy code with .NET and port as you go. This applies to MS applications as well - if it ain't broke don't fix it....
As for XCode playground... Nothing new there either. Let me introduce you to the F# interactive console that has been part of VS for quite sometime - and is a feature that will probably be available to all .NET languages in the next release of VS because of Microsoft's Roslyn (compiler as a service). The fact is that while Swift and the tooling is nice - and I'm sure will be well received by those that use XCode for their development - it is no way new or revolutionary. There is nothing wrong with that - improved tool set is improved tool set, they are just bringing development for their platform more up to date.