GK106 isn't canned. Last two conference calls have stated that they are supply constrained, and last conference call hinted at Kepler products hitting all the important price points below $400. But when there isn't enough supply, it's best to allocate to whatever makes the most money. In this case, GK104 makes more money per wafer. GK107 is necessary to finalize all the design wins and supply all the OEM's / Vendors for the new laptop refreshes (new GPU models are almost always a must with laptop refreshes, hence the reason there are so many rebadges).
The gtx660 OEM exists because Nvidia is using as many dies as possible as a functional chip from their GK104 wafers. Nvidia binned so many different chips from both GF110 and GF104 that it got pretty ridiculous (4 desktop GF110 skus, 4 desktop GF104 skus). With GK104, now they have 4 skus coming from 1 chip, so it's safe to assume they are using almost the entirety of each GK104 wafer, with half (or more) of each chip in a $400+ video card (i.e. high dollar, high margin). GK106 will be, what, $220 at most? Almost half of what a gtx670 goes for. With the same PCB and vram costs as a gtx670, the margins are much lower and they won't pull in as much money per wafer even though the chip is smaller would yield more video cards per wafer than GK104.
When the constrain eases (which is probably going to happen very soon thanks to AMD's price cuts), Nvidia will get GK106 out. The rumors at the end of July were for a September launch. I still think that is going to happen.
