I spent time actually reading the details of the patent in question here and I uncovered some interesting things.
#1 - There is a 9-way pressure sensor underneath the control unit slots. What this means is that whatever is slotted into the control unit will always have a pressure sensor underneath it. It will know whether the control unit is there or how hard you press or tilt a particular control unit.
#2 - The handheld can identify the control units because like Amiibo they can contain and store information about themselves. You could even store settings information for a particular control unit on a per user basis, parental controls on a control unit is also possible.
#3 - Each control unit has an antenna embedded into it that allows them to be powered wirelessly by the handheld. Think how mobile phones can be powered remotely. Only a couple of centimeters. But it means that the buttons could light up or spin or all manner of strange ideas. This explains the new type of rumble that was reported on.
#4 - Amiibo (maybe smaller ones) can be slotted as a control unit and used as a controller input. How? Think of the amiibo as a joystick. Using the 9-way pressure sensor underneath, you can press the amiibo forward to move the character forward. With the induction power, it may be possible to have electronically powered amiibo.