Comment 13 for bug 42678

It's not a question of hard, it's a question of priorities and whether anyone's stepped up to do it. That's generally the case with open-source. Most of the work is done by volunteers, and if no volunteer does it, it will take a long time to get done, if it ever will be (this will be at some point, I'm sure). It's been implied that it's not so simple (for whatever reason) as just packaging the xorg.conf hacks that people have been passing around. If it requires significant code modifications to X.Org, or writing extensions, or whatever, it does not necessarily qualify as easy. That it's been done by others in a totally different environment doesn't mean it wouldn't take three weeks of a few people working full-time to get working on X.Org. I don't know, I'm making no assumptions about whether this is easy or hard or reflects incompetence or good prioritization, or anything. I haven't looked at the code, and have nothing to do with Ubuntu except using it and participating in bug reports.

OS X does not use any X server protocol. It uses its own proprietary API, apparently (from Googling) called Quartz, although maybe that's not analogous to X, I don't know. It definitely does not use X.Org or XFree86 or any other X by default, although you can use them if you want instead of the defaults, since it's Unix-like.