Looking to beat AMD to the punchline, ASUS is reportedly working on a dual-GPU chip based upon the HD 7870. This would be ASUS's second dual-GPU chip of the year. The card will be based upon the "Pitcairn XT" as opposed to "Tahiti XT2" which powers the 7970. It is likely the case that they don't want to create competition for the MARS3 they released earlier this year.
Furthermore, there is somewhat of a pricing gap between the $650-800 range and using dual-7970 cores would cause the price to exceed that range. Using 7870 cores, however, places it squarely into that range as the 7870 retails for $350. The card will out-perform any single card solution while retailing for much less than other dual-GPU solutions.
The card is said to feature two full 7870 cores with all of the stream processors and the full memory bus width intact. Clock speeds have not been finalized, but we do know that the card will ship with 4GB of memory, 2GB per core. The card will use two 8-pin PCIe power connectors and has an estimated TDP of around 300W. The launch date is unknown at this time.