Well it's gonna be a real achievement for nvidia if they do, cuz they have to keep power consumption under 300watts. With two fermi's, sounds difficult. But they did pull the gtx 295 off even when people said they couldn't.
Heh, that's potentially 700 bucks for the 5970! Wow does your dad know they run that high? Also, make sure your case can fit the cards. I know that for mine, with the 5970 and 5870, I'd have to reorient Or probably cut part of my hard drive cage or get watercooling for a thinner heatsink spot.
Right now I'm "testing" my moms gts 250 (excuse for sli for a few weeks before she uses the old pc) sli has a few more hiccups though. Furmark doesn't reapply support multiple gpu burning, so I had to swap them severaltimes to get the best oc's. Then I got bsod's this last week from too high of an oc on my mom's gts. Never bsod'd with one gpu. It'd get artifacts but the it wasn't inconvenient to just turn thingsdown a bit.