I think you can be safe for several years.
If Microsoft would use something different than DirectX in a few years,
then no engine will work, whatever you may choose, even blitzMax with a DX-render engine (unless OpenGL will still be supported).
I don't think they will do that.
Every other company would have to re-design their engine to work with the new system, same as all graphics cards.
Even if microsoft would do this, you could still install DirectX9.0c and you're fine, unless the processor-code and every other driver for every component in your pc uses new code.
If Microsoft would use something different than DirectX in a few years,
then no engine will work, whatever you may choose, even blitzMax with a DX-render engine (unless OpenGL will still be supported).
I don't think they will do that.
Every other company would have to re-design their engine to work with the new system, same as all graphics cards.
Even if microsoft would do this, you could still install DirectX9.0c and you're fine, unless the processor-code and every other driver for every component in your pc uses new code.