I've been thinking about this type of system for a while, mainly due to threads like this one. Here's my proposal:
- Size of a 3DS XL, but slightly thicker to accommodate second set of triggers (either uniformly thicker, or a "lip" near the top) and a second circle pad.
- Uses technology similar to the Wii U to project the top screen image to an HDMI dongle.
- Can sync up with other wireless Nintendo controllers, such as the pro controller, for multiplayer. (don't want to lose Nintendo's local multiplayer titles, after all) Its motion controller option is redesigned top use a magnetometer to recalibrate rather than a sensor bar.