That Nvidia will launch a dual-GPU graphics card based on Fermi is more or less a given. The problem is that the GF100 GPU used by the GeForce GTX 400 family consumes too much power to be an alternative. Hot rumors (pardon the pun) is suggesting the stripped down GF104 will be the rescue. According to leaked Chinese roadmaps Nvidia skipped the original D12U-50 card with dual GF100 as it would consume up to 375 watt.
The plans are instead to launch a model sporting dual GF104 circuits, code-named D12U-15, which should consume a lot less power. When the card will appear and what kind of performance to expect is uncertain. The rumor suggests a launch for Fall and that the GF104 circuits are the same we will see with GeForce GTX 460 next month, peaking at 150 watt.
GeForce GTX 465 that was suggested earlier will instead use the GF102 circuit and peak at 200 watt TDP.