Before the Switch announcement, there was a lot of discussion over a patent Nintendo filed for a tablet-like system that featured detachable controllers. The controllers had no electronics in them, but instead used an infrared camera inside the system to "read" from the buttons and joysticks in the detachable housing.
What if this was a stealth-patent for a Joy-Con accessory? The Right Joy-Con could be socketed into a device like the Wii Zapper, except that this new device features additional buttons and joysticks which are read via the infrared camera. (Aiming the zapper would be done with gyro controls).
This "Switch Zapper" could be a cheap plastic shell that instantly adds a bucketload of functionality.
I imagine other specialty controllers could be designed in this same manner.