Some people probably said that about the .NET framework. Now almost all of it (the new stuff anyway, and minus Visual Studio) is fully open source.
If someone is licensing something under GNU GPL, they are also giving away their intellectual property/patent rights (or what ever they call that) to any software developed in GPL, which Microsoft is never ever going to do.
MIT/X11 license is not giving other developers and users such a patent protection from its original developers.
B) Modern MS-RSL "reference source license" is now OSS compliant. The remaining difference between .NET Full Framework's Reference Source and what's happening with .NET Core is .NET Core has moved development to the open and Github as primary development platform. .NET Core is the future and .NET Full is "stable".
C) One example: http://referencesource.microsoft.com/#PresentationFramework/...
There's nothing stopping you from using the Reference Source today to build your own WPF fork (or, let's face it, you probably mean SWF). You can even start with Mono's existing mostly-there cross-platform SWF or Moonlight codebases and save a bit of time.
You know why you don't hear about lots of people doing that? I'm fairly certain it is because no one is building cross-platform GUIs in anything but HTML(5) these days.
https://www.gnu.org/licenses/gpl-faq.en.html#DoesTheGPLAllow...
I'd argue otherwise[1].
Also, as of ~2 years ago, CentOS is just another Red Hat supported project.
