Windows has its own legacy baggage and I wonder about the proposition that the mobile OSes' Unix underpinnings aren't relevant. Depends on what you're doing, I'd think.
Windows might have its own baggage, but with Windows 8 they have brought the original design of .NET from the ashes and assuming the current path is to maintain, those of us that like Windows will have a nice OO ABI alongside safe languages compiling to native code.
All the mobile OS relevant APIs don't have anything to do with UNIX.
All the Objective-C, Swift, Java, JavaScript, C++ APIs available on those OSes don't depend on being implemented on top of an UNIX kernel.
I mean .NET Native and the lessons of Midori finding their way into C# 7+ and C++/CX, alongside with emphasis on the C++ Core Guidelines, which started at Microsoft before Bjarne got involved.