So if it actually is anything like Eurogamer suggests, I'd like to see something along the lines of this:
Form factor similar to the below pictures, although I'd have the following:
A) Clickable snub Analogue Sticks as opposed to Analogue Sliders.
B) Shoulder button, but a cross between a smaller version of the Gamecube button and a scroll-wheel. So it scrolls and depresses to a click.
But having seen the following picture I've also had some more thoughts...
The screen part of the portable has a sensor bar. You dock the screen, connect it to the TV, upscaling occurs, and you use the 2 control parts of the device like Wiimote+'s but with all the button as I said above.
So effectively you have a HD super-Wii, which has a relatively traditional method of input too:
2 clickable analogue sticks
D-Pad
4 shoulder buttons (2 of which are a scroll)
4 face buttons
...all on 2 motion sensor control parts. Throw in a camera on the back of the screen section for some AR gaming (Pokemon) whilst on the go and voila!
EDIT: VR, ala mobile phone VR, as per what @dazzybee says below too...
That's my dream (with OS level Party Chat of course :p )!!!
So essentially this: