You just described the "xMac", the code-name that all the fans and nerds used for the computer they wished for during the 'aughts. And I think there's some pos

You just described the "xMac", the code-name that all the fans and nerds used for the computer they wished for during the 'aughts. And I think there's some possibility that a computer like this is on the horizon. Apple wouldn't announce a feature like first-class external GPU support unless they had really big plans for it. Maybe the new Mac Pro they promised will be more like what you're envisioning...