[delecti]

All it does it confirm that they have something there. The Wii used a sensor to detect where it was pointing, the Switch had an IR camera for a variety of weird gimmicks, the NES and SNES had light-detecting "guns". Hell, it could even be an IR blaster like the Wii U Gamepad had, and not a sensor at all. We just don't know yet.

[vel0city]

The trailer shows the joycons sliding on that side with an additional attachment (see: 1:10). It seemed pretty obvious they were trying to hint at some kind of mouse-like optical tracking on a flat surface.

https://youtu.be/itpcsQQvgAQ?t=70

[delecti]

That could well be what those are, but to me they just looked like the wrist-straps, like the original Switch has. https://www.nintendo.com/us/store/products/joy-con-strap-gra...

[klausa]

They're both.