I think that there is an error of analysis in the equation…
In spite of its energy efficiency, X will tegra it remains a large electricity consumer… One will need a large battery, therefore a large portable console, with according to eurogamers, an active cooling system!
The market of the portables aims mainly young people… Will Nintendo try to sell to the parents a portable with 300€? There is nona direction… There is not really again concept…
I think that tegra X will it is not in the portable part, I think that tegra X will it will be in the fixed part (connected to the TV) that the lever will be close to the illustration of eurogamers, it will be a small screen device (see a smartphone or in any case compatible 4G) with 2 “Mix of Wiimote/nunch” which would be attachable on the sides of the small device, This device will be probably also equipped with Nvidia equipment but much less powerful than X1 will tegra it (the k1 if my memory is good, approximately 300 GFLOPS) and of ARM to ensure autonomy… the screen device (or the smartphone) + controllers detachable will form a portable console.
But I think that they will have there a system of cloud and of streaming gaming between the part fixes (container will tegra X1 + Hard drive) and the screen device , a system allowing to exploit home's games in streaming the portable part via wifi and Internet thus unbounded of distance starting from a connection wifi.
In short:
A fixed part, comforts home console and personal server equipped with will tegra X, hard drive, and of ports cartouche a moving part which will be a screen device or a smartphone with approximately 300 GFLOPS for graphics, but able to receive/send data or a flow streaming via wifi (see 4G) towards / from the fixed part. The last part being the pad which seems to be made up of two Wiimotes news, probably with stick analogical, which sticks on the screen device /smartphone to form a portable console or a gamepad…
In this manner, Nintendo will continue to make games smartphone, games portable, games living room but all will leave on NX…
