Your predictions for the most under utilised aspect of the Switch?
Nintendo hardware often has interesting little features that go massively under used, or used only for pointless gimmicks.
As far back as the GBC there was an infra red port, the SNES had the super game boy, the N64 had the expansion port which led to the stillborn DD as well as the GB transfer pak, the DS had its touch screen which became shovelware, card games, menus and name entry after an initial burst of bad features (recall Castlevania ice sections and seals), the Wii had its remote dubbed waggle controls for a reason, the 3d of the 3ds ceased to be mentioned after about a year and "the Wii u".
Now that we have seen a few Switch games, got a feel for the hardware and can look to what is to come what then do you think the Switch will have as its equivalent? Will its joy cons be controls that can be detached to go into another holder, never to experience "HD rumble" or tilt sensors? Will handheld and docked mode be slightly different clocked versions of each other? Will its online services be the domain of score boards and DLC?
Edit. As many have mentioned the infra red camera is most likely to be the main one, if you want to skip that in favour of the second or third place ones then feel free.