Even if its technically possible, why would you want that? I recently bought a Gsync monitor and I can barely tell the difference between 60 and 120fps, while I had to use the lowest graphics settings to hit that 120fps.
At this point in time and even more by the time the Switch' successor comes, it will be smarter to bet on a chip and display that are capable of VRR (Variable Refresh Rate) like the XBsX and PS5. No more 30, 60 or 120fps, just constant smooth gameplay.
I doubt that Nvidia will invest in mobile GPUs at this point. The Tegra never really caught on in mobile: the Switch is basically the only customer for it.
Nintendo will need to find another vendor for the next Switch (of which there are plenty in the mobile space).
Nvidia is still interested on mobile GPUs, and this article from last week proves it: https://wccftech.com/nvidia-geforce-mx-400-turing-notebook-gpus-tackle-intel-xe-dg1-and-amd-vega-igpus/
As for going with another partner, it is possible but not likely. As MSoft with the first Xbox and Sony with the PS3 learned, it's easier to deal with only one provider rather than with two. Not only that, but this also has other benefits like tayloring both the CPU and GPU to minimize bottlenecks.
Because of that, and because AMD has no experience with ARM processors and their GPUs still use more power than Nvidia's, is why I think Nintendo will go with Nvidia once again for their next machine.
Please excuse my bad English.
Currently gaming on a PC with an i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
Steam / Live / NNID : jonxiquet Add me if you want, but I'm a single player gamer.