10nm already is on the market to OEMs, in fact is moving to it's 2nd stage.  By the Switch launch date it should be quite viable to use.
If Nintendo does not choose to use it, it is simply down to cheapness and aversion to cutting edge tech.
Switch is already known to be custom silicon, with totally different GPU than X2 (originally announced as 16nm).

IMHO I don't expect more CPU cores, simply because programmers have been unable to fully leverage so many cores.
That is what happened to PS3, and likewise we don't see Nintendo going for more cores than Xbone/PS4 despite years of progress in arch/fab... Likewise for Scorpio.
Obviously GPUs are another story than CPUs.

I don't see the big deal on AMD vs. NVIDIA GPUs here, obviously the latest of either is better than older gen stuff (ala OG Xbone/PS4).
AMD's architecture is great at new features as seen in DX12 and that is what consoles are leveraging as well.
All in all, I don't see some big story out of Nintendo/NVIDIA collaboration here, if it does well certainly expect an "update" of arch, nothing new there.

At this point that is all the companies want to do with hardware. Every few years we will see new iterations from all three companies.

Nah you don't say a console is more than a GPU, considering the CPU in PS4 and X1 are eseentially chips that normally are in mobile I don't think you really can boast about great CPUs for consoles in that regard, considering the debate is about GPUs that's a bit null and void as well.

You act like MS and Sony have never opted to utilize different companies for components, 360 from Gen7 did it just fine, companies will go with they feel is best, AMD being convenient doesn't lock the console market to them.

I read that TSMC was going to bring 10nm by the end of this year with volume production in 2017, but after the fiascos they got with the latest node transitions, I don't know if that's still true or there have been delays.

In any case, 10nm right now would be more expensive and with lower yields than 16nm, so Nintendo will probably avoid it right now.

About the ARM cores, I didn't mean to say that they would put more cores into the hypothetical Switch revision, but replace the existing ones with newer and more efficient cores. The standard Tegra X2 comes with 2xDenver 2 and 4xA57 cores. We don't know if Nintendo's customisation has changed that configuration (they could have gotten rid of one or two of the A57 cores to put some fixed instructions, like they did with the Wii U processor), but a revision could see the A57 cores replaced by newer processors for more performance but also increased efficiency.

Scorpio is rumoured to have an 8-core Zen CPU. Trust me, you won't find such a thing in mobile. Xbone and PS4 are bottlenecked by their CPUs, but that's partially because AMD had inferior tech in the past. With the new generation of CPUs, they'll be able to push consoles that much further - and still, nVidia isn't even in the same ballpark when it comes to CPU performance as the old AMD CPUs. Doesn't matter what the debate is about, the CPU part makes your speculations null and void.

Sure. Many strange things were done in the past, in the PS2 era a console being unfriendly for developers and hard to write games for was seen as a good thing. Sony could get an nVidia GPU and tell IBM to make a Cell 2 and make the PS5 costs $1000 to manufacture again. But guess who'd win that generation if MS went for cheap off-the-shelf SoC parts from AMD? Competition may always arise, but as for now - there is no company remotely close to being a viable alternative. Especially not when Polaris is on par with Pascal and Zen is in the same ballpark as Skylake. AMD is at a really high point right now, it'll take a very strong effort to take the home console market away from them.