I've said this before DS/Wii/3DS were one off proprietary techs with dead end family trees. Wii U too if you count its PPC cores. It was very much using customized old tech to fit Nintendo's purposes.
Switch will be the first hardware design Nintendo has had since at least the GameCube era where there is a reasonable path forward from R&D being done on the chipsets the Switch is using. More importantly they have a big GPU manufacturer on their side to design the thing rather than going it alone as they did with the Wii and Wii U.
Tegra X2 SoC and its potential successor remains formidable in the space Switch is operating in given they inherit or will inherit the DNA of the desktop GPUs, a space nvidia dominates. And now that Switch is successful, nvidia and Nintendo have every incentive to do a true next-gen Tegra SoC tailored to conolse/hybrid use with multiple popwer profiles rather than re-purposing a very powerful SoC initially targeted at the mobile space.
I guesstimate Switch Pro needs to be 1.5 -2x the power of the Switch (X2 fits the bill) and a true successor needs to be around 4-6x the power, somehwere in the 1.5 - 2 TF range (Nvidia flops, so probably much closer to 2.0-3 TF when comparing to the current AMD consoles) though naturally a next-gen tegra will be several generations more advanced architecturally as well when comparing the PS4 or XONE
The sky is the limit and to be honest, the only people who can fuck this up is Nintendo.