1. Switch2 SoC is custom and exclusive to Nintendo
2. RT and DLSS HW are Ada gen, not Ampere
3. You can't compare with Windows desktop GPU because even minimum RT effects are well above current consoles.
4. As said, RT is very scalable. Quarter/Half res effects in association with DLSS are the target. Many games will come with it at 30+ fps
1 - Correct
2 - Can't prove or disprove. But I'm inclined to think it's true, even if only small and slight modifications, given that the NVDEC/NVENC, Engine CG, OFA, etc are all Ada Gen rather than Ampere Gen. T239 Compute Capabilities are also 8.8 rather than Ampere 8.6 and Orin 8.7. Closer to Ada 8.9.
3 - Exactly. NVN2 documentation files provided a RT sample where you could toggle to cut the RT resolution in half and then use DLSS to scale back. I also think that T239 more performant OFA (Compared to Ampere OFA) is to aid Ray Reconstruction (FrameGen is too costly compute wise).
Unlikely. Can't see Nintendo swapping out Ampere's RT engine for Ada's... esp when it's most likely to be on Samsung 8 nm anyway.
There are multiple block that aren't Ampere or Orin/T234 on T239. Tensor and RT Cores wouldn't be far-fetched, although I do agree that it would be a much higher level of customization effort. If what xpea said is true, I think it's probably some smaller modifications to the TC and RT units.
As for foundry, I'm not assuming anything at the moment. It's a custom design for a specific client and isn't bound to anything pre-existing. 8nm is likely, but who knows what Nintendo will want.