I'll share my wildest idea yet, what if the JoyCons sides are modular, or more appriprately, extendable, not the JoyCons it self having a SCD, but that you could buy separately, extra "JoyCon shaped" Expansion units that you would attach on the sides when you don't need the JoyCons since you're docked, and you could buy ones with more RAM for example or more CPU, but I think for simplicity they may come with a SOC, of 1 ARM CPU with 4 Cores, and let's say 1GB of more RAM and sold for 30 dollars for example, so the SCD connector could be hidden in there where the JoyCon attachments are, but more deeper inside the rails, but the JoyCons wouldn't use that extra high-speed bus, they would just use their own input connector also in there that we can't see.
We could be in for those Expansion pack & Rumble Pack times again. The joycons could actually be purely wireless without needing the input connector, but im not sure how well will that go with hardcore tournaments if the lag issue isn't fully optimized. The Pro controllers could have an option to be wired through their USBC and to the Dock external USB port.