Even this new forecast is too high, it can still drop more in weekly sales and has a long way to go to reach anywhere near 3.5 million sellthrough. At this point, managing 4 million shipped will be impossible, the stock is overflowing in most stores, they simply can't force their surplus onto retailers and warehouses unless they move in retail and there's an actual need for more stock.
At this rate, they'll likely miss the shipments by as much as 5-600k and will be lucky to move significantly past 3 million in sellthrough, far away from the intial mark which would likely be 5 million (assuming a 5.5 million shipment total and normal sellthrough rates this time of year). The demand is simply not there and appears not to be forthcoming for some time either.
After the Wii shortages, who would have thought that excess stock right after launch could ever be a problem for Nintendo? I honestly expected the Wii U to perform better than it has (even if I was being somewhat conservative).