So according to this documents (
Don't take every feature listed as a guarantee for what will be in the final product)
On the tablet:
- Downclock when working on portable mode.
- CPU fan that works in portable/dock mode and regulates RPM accordingly.
- SD storage plus internal storage.
- Possibility of HMD use with a Head Mounted Display - VR helmet.
On the dock:
- The tablet is not downclocked anymore in this mode.
- No secondary CPU fan.
- USB-C port for charging and communication with dock.
On the joycons:
- Can be used 4 joycons per device.
- Clickable joystics.
- Hidden shoulder buttons on the connection side.
- Hidden leds on the connection side.
- Leds show player num. and battery level.
- Possibility of different joycons usable (ex: with d-pad instead of buttons)
- IR sensor for pulse detection (not sure if also for pointing purposes, the patent talks something like the vitality sensor)
- Accelerometers and inclination sensors (pointing could be done with this nowadays, plus the other common uses)
- Left "home" button is refered to as Record button. "Record image" possible. Maybe video, but its not talked about and could just be screenshots. Technically, Flash storage is not a limitation nowadays in regards to use degradation (think smartphones with internal memory only, for example)
- Joycon grip includes battery. Able to charge joycons or make their battery last longer.
- Communication to the tablet via Bluetooth.
What am I missing? Tell me and I will update.
Edit: Corrected some things, also, here is a better list:
https://www.reddit.com/r/NintendoSwitch/comments/5ii58o/nintendo_switch_patent_megathread/