Still holding final initial thoughts until we actually get the real information about the next Nintendo console, but here are initial thoughts.
Wii "Casual" customers upgrade habits are a big if. No guarantee that these customers upgrade quickly if at all. They could be people that are happy to play Wii Sports for years.
Touchscreen controller makes playing games more complex. Part of the comfort of a controller is you learn where everything is at and then you really never have to look at the controller, your muscle memory knows where the buttons and sticks our. If I have a screen that I am not looking at because I am focused on the main action on the TV screen the touch screen becomes a nuisance.
Slightly more power than 360/PS3 doesnt do much for the Nintendo next. Sure they may get some more late generation ports (not all because the userbase will just not be that large). But why would someone be all that inclined to pick up the Nintendo next for that. Hell 360/PS3 will be $100 to $200 cheaper by the time this releases. Also with the power being roughly the same MS/Sony can release add-ons to the 360/PS3 that mimics whatever Nintendo comes up with (controller wise) and still be cost competitive.
If Nintendo isnt using the motion control games as the selling point and going back to Mario, Zelda as the reasons to purchase this console then they are just going after the customer that they already have locked in. The 1st party games that truly made a difference were the motion controlled focused games.