Isn’t backwards compatibility one of the tentpole features of Windows? If you meant future versions of apps, sure, but I’d otherwise not expect this to be a problem in any significant sense.
It’s forwards compatibility if we’re discussing the idea of the program being compatible with future versions of Windows, but that’s neither the point of what was suggested, nor is it realistic — breaking changes, or compatibility, are going to be at Microsoft’s hands and largely an intentional decision at a platform level, not something an individual developer can shore up against.
It was. A long time ago. Running old games on Windows has become challenging.