I would be a little surprised if they switched off of ARM. Even the Steam Deck with its custom AMD SoC is much closer to laptop specs and wattages than the switch e.g. 20w+ SoC, more than 2x battery capacity vs Switch. The switch has a lot more in common with phones than it does with other consoles or PC portables so IDK if we will see AMD SoCs with the right power profile for nintendo's needs.

Nintendo could use one of the new Samsung SoCs with RDNA2 graphics though. Those could be pretty good competition for Tegra X* chips.