It won't run Doom.
Apple's biggest mistake was not the open architecture thing. It was the games. I couldn't play Leisure Suit Larry on the first Mac, so I didn't buy one.
Not natively.
I really do think that it's not the architecture, it's "Follow the Money"
It makes more economic sense to develop PC games because most everybody uses PCs. Suffice it to say, Mac only has a small percentage.
If they can't develop a hybrid version or have the resources to develop one version--they're going to develop the game for PC.