This is what Nvidia does for a living. The 7950GX2 was their answer to the X1950XTX... couldn't get a decent card with a single GPU, so they stuck two together instead.
Seems they're doing te same with the 8800.
The cooling won't be a problem, me thinks. The 65nm 8800 doesn't seem to be bothered about heat at all, so this cooling solution will still work. I'm sure that cooler might even get better temps than the stock 8800GT one, since that fan looks like a very big, very chunky fan. If the new bigger fan on the single-slot stock 8800GT cooler is anything to go by, this might be a slow-spinning fan, trying to keep the noise down, and only just keeping the cores alive (since the 60mm ran extremely high speeds, to keep the GPU at, say, 83c, and made a hell of a racket, with the newer 70mm model capable of keeping the GPU a little tiny bit cooler, at ~80c but at much much lower RPMs, and hardly audible, second what the released materal stated).
Replacing the cooling may be trouble, since the two GPUs are facing each other, and that ribbon cable connecting the PCBs doesn't look like it likes stretching (hell, looks flimsy enough that it might come out while putting on the stock cooler, much less after-market).
Watercoolingwith a single replacement block in the middle is definately a possibility, and someone's probably already thinking it up.
I must say that the ATi arrangement for the 3870 X2 looks to be much better, in terms of simplicity, and in terms of having a tidier layout (no chance of misplacing that second PCB layer, when doing maintenance). Yes, on air cooling the second GPU will be receiving the hotter air, but I'm unsure if it will make such a large difference. Watercooling meanwhile should be a piece of cake. Just get two seperate waterblocks, like the Maze 5, along with two packs of RAM 'sinks, and a low-profile chipset 'sink for the PCI-E switcher between the cores.