The handheld/console hybrid has been Nintendo’s dream for a long time. They even merged their handheld and console development teams a few years back, so I can’t see them abandoning the formula.
The only way I can see iterating on the Switch design is by dropping the dock in favor of a tv dongle to connect and stream wirelessly. This could allow for asymmetrical gameplay much like the WiiU (and would open the door to WiiU ports).