Do they not have a dual GPU version of the 280 then?
No, the cost would simply be too high. It would almost definitely have to be a dual PCB board, not a single PCB like the X2. Two 512bit PCBs would be very
complex and expensive. Not to mention the power requirements and heat output.
What I think we might see, is a dual GPU GX2 card made with the 55nm G92b with higher clock speeds and faster GDDR3 memory.