I've taken the Joycons apart, and they actually look like really good quality components. The factory setup is highly integrated and looks much better engineered than, for instance, the controllers in Ben's linked vid. I was curious what micro and gyro chip they were using, but the board to board assembly is to sophisticated to justify disassembly just for the sake of curiosity.

I'm the guy that did the schematic for the Nintendo Game & Watch hack, if you happened to follow that one on YT. The joycons share some component parts with the G&W. This is how I figured out what some stuff was in my G&W schematic. The joycons are much more sophisticated than the G&W design. I was surprised at seeing that. The Hori controllers are stupid simple STM32 with basic designs.