Today NVIDIA lifts it's NDA on 3 way SLI. Although it seemed to have rushed it out ahead of it's competitor AMD+ATI, it doesn't seem to appeal to most gamers. This is largely due to the fact that you need to use at least 3 x 8800GTX to achieve 3 way SLI. You can do that with lower end cards like the more affordable 8600 series.
NVIDIA marketing is silly to launch things at year end when Christmas is round the corner. Press can't get 3 cards and 680i board for review too. So, what is the point ? Even you can get 3 8800GTX cards, you will have to look for a 3 way SLI bridge. Of course you can choose to connect the 6 connectors crossing one another as shown in the review (ref) we posted earlier.
Even with 780i, I doubt 3 way SLI will be the way to go. It is simply to milk those rich kids who wants the best of best without considering hardware depreciates faster than anything else.
I will assume that there will be 3 way SLI without the need for SLI bridge. It is only a matter of a small performance hit. Whether NVIDIA will enable it really depends on how AMD markets it's CrossFire X which allows even HD 2600XT to run in tandem.