Their options are: Tegra Orin, AMD Phoenix Point (Successor to Rembrandt), Intel Raptor Lake (Successor to Alder Lake), Snapdragon 9/9+, Exynos 2300 or it's successor (Has RDNA2 cores.)... The other ARM manufacturers aren't on the same level with competent GPU's unless it's licensed from another party.
I doubt they will go much newer or older than these.
Seems they had a better experience than Microsoft or Sony with their chip supplies, so the possibility of nVidia being the partner again is real.
...But AMD is also not the same AMD either. Rembrandt has proven they are extremely competent at making low power SoC's.
I think the best thing we can hope for is capabilities that are a little better than the base Playstation 4, sort of how the current Switch is better than the Playstation 3/Xbox 360.
I wish Apple's M Series would be an option, would be a monster console if you develop games specifically for that chip.
I kind of remember a partnership between Nintendo and Nvidia for 10 years, what I remember is that before Switch release, Nvidia Expected a 20-Year relationship with Nintendo, I guess they are expecting 3 generations of Switchs with Nintendo. (Switch, Switch U & Switch One)
But true, I can see the Next console beating PS4, getting results closer to PS4 Pro, thanks to the new arquitectures and developed capacities for the new generation processors.