So a bunch of Nintendo Switch patents were filed and give some insight on some features Nintendo hasn't revealed yet.
(If you really wanna read the whole thing)
Nintendo files multiple Nintendo Switch patents (controller, dock, architecture*)
TL:DR
Right Joy Con has NFC reader
Right Joy Con has IR pointer at bottom
Both Joy Cons and the Switch itself feature Gyro sensors
Joy Con Grip houses a battery pack
L and R shoulder buttons are on each Joy Con
Up to 4 Joy Cons can be in use on a single Switch.
Joy Con triggers are analog
Games WILL be upscaled when docked
Joy Cons come in multiple "styles", some with proper D-Pads, some with no analog sticks
Switch screen is a touch screen
Record/share button
VR compatibility (maybe in the future)
Wired and wireless internet connections (i know someone here is gonna be happy to hear that)