Umm sorry for the sudden bump, but this one is a big interesting what if
In 1990, a then-unknown Id Software approached Nintendo about the idea of porting Super Mario Bros. 3 to the PC. They manage to Partly port a level of SMB 3 to IMB PC clone EGA PC without any techical documentation: http://www.youtube.com/watch?v=cj4HJkeQSg0
In our world, Nintendo declined. Id went on to make Commander Keen instead, and from there they went to make Wolfenstein, Doom, and Quake, practically defining the FPS And PC gaming as we know it. But in another timeline...