There were Voodoo2 SLI, but the time to make Voodoo Banshee was a long one. I think that if they were to release a Dual-Chip Banshee, they would have some low-price competition for the TNT.

Voodoo Banshee proved that even witout Multi-tex, it could even outrun some other cards. Also, the Dual-Banshee would have been the solution to enter one of their first 32Mb video card, and make a performance near to the Voodoo2 SLI, at a much improved quality. And the price would be near half of a V2 SLI. The board would have been a bit smaller than a V2, and with Multi-tex, before the V3. Which would surely be a major kick for Nvidia.

I think a dual Banshee Board would have been quite hughe, and expensive....

Even the Voodoo5 took many revisions (and costly delays, which ultimatemy added to 3dfx' demise) in order to get SLI work correctly (and this after so many years of SLI experience). It ended up still as a fairly big card.

IHMO, it would have been a monster of a card (for the time's standards), and too expensive to manufacture.
(would have made for a nice collector's Item though ;) )