It will probably be priced somewhere between 2x 6950 and 2x6970. The top end dual gpu card has never cost more than 2x single high end gpu cost, and has always had an rrp of a significant saving over 2 single high end gpu's, though the rrp for the 5970 was £440, and you could rarely find it under £540 for the first 4-5 months, that shouldn't happen this time around. Remember that 2x5870's were £600 for a long time so £440 rrp was a massive saving(£40 more than 2x5850's).
Though its probably worth waiting for because it could push prices down across the range. IF the 580gtx is soundly beaten, its price could come down, as could the 570gtx, the 6970 and possibly the 6950. If you're building a rig from scratch you could well be better off buying a decent design mobo with 2 spread out pci-e slots, two custom and better cooled 6950's.
The 6990 and most certainly anything Nvidia release will be SO close to the pci-e 300W spec they are more likely to be cut down further than any previous dual gpu card, two single cards will almost certainly overclock better and offer better performance.
Honestly theres very little reason for a single card setup these days unless you've already got a single pci-e slot computer and only want to upgrade the gpu.
If you were after better value, 2x560gtx in sli or 2x 6870's offer exceptional value/performance and great xfire scaling. Depends what you use them for, gpgpu work you can only go with the high end cards, ultimate performance, go with the higher end cards, great value and "good enough" performance, the slightly lower cards are a better choice.
