This is a weird one, but I’d love to see a reimplementation of the sensor bar. The gyro controls haven’t cut it for me. I like how the Wii U game pad had the sensor bar built in to the bezel. The real engineering nightmare would be squeezing IR cameras into the top of the Joycon
It would be cool for the 3D display tech to get an improved implementation on the Switch, but whether it’s worth it will depend on how much cost it adds to the system and how much it lowers the resolution. I did enjoy its use on the 3DS, but I often play the Switch in docked mode and I’m not sure I’d like to pay extra for its inclusion on the Switch 2.