How could you have upgaraded or even the same Wii U specs at $150? even if you knock off $100 for the game pad your still at $250 or close
Wii U is currently $300, it could very likely get a $50 price cut this fall (I'm guessing in September to go alongside Mario Maker) bringing it to $250. Shave off another $50 by getting rid of the Gamepad so now $200. Wii U also uses exotic components that aren't mass produced making the console cost more than it needs to. All of this plus were looking at a launch 12-18 months from now and $150 really isn't out of the question for a device slightly more powerful than Wii U.