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
Backwards compatibility is the big one, especially cloud saves. I’d settle for native Switch 1 performance as long as every Switch 1 game worked properly.
Yeah, backwards compatibility is the single most important switch successor feature for me.