I was thinking to myself today, and I think I know what the NX will be
If you remember the "weird shape" touchscreen concept that was brought up in this thread earlier in the year, I'm guessing that was just a general proof of concept. However, I still believe it will be used in the final product.
The NX will be a traditional rectangular shape. However, the screen will take up the entire front face. It will most likely be 16:10 or 16:11 to accommodate for the four modular control notches cut out of the four corners. It is here that the free-form touchscreen will come in; the screen will continue around the controls and show HUD information pertinent to each control in every corner. This is where my theory ends if the console is purely portable.
However, my speculation continues if the console can be docked for extra power; if this is the case, the device will have either a micro USB port or a proprietary port on the bottom, and will slide into the dock much like you slide a power drill battery into a charger. From here, a faceplate can be added to the top over the screen if you do not merely wish to charge it; this will convert the four input modules into four controller ports and shut off the portable screen for maximized efficiency. In this mode, you have a decently powerful home console with a very small footprint