While viewing Rogue One, there was a scene in that film that made it all click together for me. I was trying to think of what docking the Switch reminded me of... when I realized the Switch is basically a cartridge itself! The Switch dock is top-loaded, not unlike the Famicom/SNES. So what do you get when you take a Switch tablet, remove the screen and battery, and fill up all that space with a 1060?
Switch+
It's not the dock that's the powerup, I believe it will be an accessory for the dock.
Enabling dual screen gameplay like the Wii U.
Enhancing the graphics tenfold.
Tabletless SKU?
Acting as a base so 8 Switch players can also use the TV as sort of asymmetric gameplay/spectator mode?
Enabling VR?