The Inq has some more info about ATI's physics solution:
Our sources claim that the concept won't be tied into the "1GPU does GPU-stuff, 1GPU does PPU-stuff", but rather sharing a dynamic load. RingBus memory controller is of course, the guilty party for making Physics & GPU sharing a reality. Even better, it will probably not be required to use two same spanking cards at the same time - shelling out 500 dollars for a GPU and another 500 for the "GPU with identity crisis" is really not a great idea. ATI's approach is set at raising the number of sold X1600 boards and getting rid of old R520 stock.