The concept is great, but it works much better ala cross-buy like with Vita and PS3/4.
Unless the handheld and home console had very similar architectures, it would crazy to expect the same code to run on both systems. This isn't like a PC in which a lower spec'd machine can run the game at a lower resolution. In the hypothetical situation that physical carts can be swapped between the two, the most likely thing to happen is that each cart has two versions of the game on it. Not the biggest issue, but it does mean devs still need to make two versions of the game.
Also as I said in padib's thread, each system has different inputs. A wiimote/gamepad centric game just can't be played on the portable. What does Nintendo do in these cases? Not allow those games to be made?







