[droptableusers]

If he knows he will be porting the game, why does he not abstract away the OS layer and perhaps even the graphics library? Then implement it behind some interface with for example SDL2 and OpenGL depending on platform.

Would not that save lots of time and ensure it works cross-platform from the start? To me, it just seems that you re-invent the wheel by not doing this.

[m4thdimention]

He will abstract it. His style is to implement first, then figure out the abstraction, not the other way around. Plus he's done this before and probably has an abstraction in mind which will make that style work even better.