It would have sold quite a bit, 50m upwards for sure. If we're keeping the same 1st party line up then that would be limiting as Wii U has a pretty poor line up compared to the wii's and gamecubes (with the same period of time)
The corner stone of last gen is that all the biggest franchises were multiplaform which is a 360 departure from what we saw from the PS2 era and prior, wii U would had tons of third party support no doubt. Don't forget the Wii had dozens of titles planned by big publishers before it was deemed a "success", and the xbox/gamecube performed very similar so they wouldn't give support to 360 but then skip nintendo.
On that basis alone it would ensure fair success (40-50m), add in the touch screen gimmick (Something that was very much new back in 2006, Iphone didn't come til 2007, Ipad till 2010) and Nintendo could have potentially mimicked the success of the wii and surpassed it LT (not profit wise) if they were able to tap into the appeal of tablets as social devices and convenient entertainment. Unlike the wii, this system would have kept selling past 2010 due its future proof tech and software support. Of course it would never peak in the same way wii did though
Price wise we're not assuming it used the exact same tech as the current Wii U are we? If its hardware mimicked the 360 , minus the HDD (flash memory instead) but with the gamepad in toe, I think it would go for $500-$600 dollars with Ninty managing the losses initially. Remember the PS3s huge price was down to the Cell processor and Bluray. Even in 2006, the gamepad wouldn't have been a fortune (<$200). Its NOT actually a tablet, its a touch screen+controller with minimal processing going on in the background.
Edit: wait do you mean the games line up would have to remain 100% the same including third party support? In that case ignore my entire post lol. It will still sell far better then the current WIi U though.







