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
This is honestly the biggest thing. I’d add Nintendo account support with the ability to bring over digital purchases to the new system.
If they do those two things I will buy the next system no matter what other things they do with it.