most of those games would have windows builds?

that said, i sometimes think about a clean-room reimplementation of e.g. the unity3d runtime -- there are so many games that don't even use native code logic (which still could be supported with binary translation via e.g. unicorn) and are really just mono bytecode but still can't be run on platforms for which their authors didn't think to build them (or which were not supported by the unity runtime at the time of the game's release).