It'd only break your code if you're using DirectX functions AND GS stops using DirectX for Windows versions. Yes, Windows.h wouldn't work on other platforms either, but there's no reason those using WinAPI functions can't stick to Windows-only if they want.

Have another read through the thread, look at the pictures, and make sure you understand the first post. That should address any concerns you have about knowing our audience, how relevant XBox and iPhone are to the discussion, and whether any of us are exploring other options.