Here is my final prediction: 

If GPU is Tegra T239:

The performance level to expect when docked (assuming 18-20W total power target) would be about 85%-90% (in terms of framerate) of a RTX 2050 mobile 30W.

https://www.techpowerup.com/gpu-specs/geforce-rtx-2050-mobile.c3859

The performance level to expect when portable would be slightly better than the base PS4, but of course with more modern features (i.e ray-tracing.) 

Over time the Switch 2 would outperform the 2050 mobile because it would have much more video memory available. 

As far as desktop GPU's are concerned, it would be somewhere between a GTX 1050ti and GTX 1650. 

IF GPU is a Lovelace Tegra or if power target of the T239-based platform is loosened to 25W-30W total:

The performance level to expect when docked (25W-30W power target) would be somewhere between an RTX 2050 mobile 30W and RTX 3050 mobile 35W 4GB, likely closer to the latter. 

https://www.techpowerup.com/gpu-specs/geforce-rtx-3050-mobile.c3788

A roughly comparable desktop GPU would be the RX 570 or a GTX 1650. 

This would put it at about (or very slightly below) the level of a Series S when docked, with the Series S more like a GTX 1650 super/GTX 1060/RX 580.  

When portable, I'd expect between PS4 and PS4 Pro performance.

EDIT: DLSS isn't magic, but it can in many cases bridge the gap between a budget/performance half-tier or even tier (i.e GTX 1650 level -> GTX 1650S level; RX 570  level -> RX 580 level; GTX 1050ti level -> GTX 1650 level, etc.) Half-tiers/tiers tend to be about 5%-15% more performance than the iteration they improve upon. That's in the realm of what gains the Switch 2 would expect to get for using DLSS over FSR and slightly decreasing internal resolution (say internal 800p instead of internal 900p/1080p by using DLSS rather than FSR; 30%-50% reduction in internal pixel-count for similar image-quality target.) 

EDIT 2: I'd expect most Switch 2 games to upscale from 720p-900p -> 1080p or 1440p in docked mode and from 540p-720p -> 720p-1080p in handheld mode (depending on the screen resolution mostly.) Some simple 2d/2.5d titles would do 1080p -> 1800p or 4k. VRR would be nice, but if there isn't VRR then we'll probably have a 60fps target for simpler games, and 30fps for graphically demanding ones, dependent on genre too of course. 

How likely is it that Switch 2 does native 16k resolution (TV, on the controller only 12k), with 50 gb ram, 10 terabytes of SSD, DLSS 7.0, all under $359.99?

Given that many titles become VRAM bottlenecked on 4GB chips these days, that is something also to consider. Switch 2 will almost certainly have more than 4GB of memory available for graphics. 

It would be wild to see what a Switch system only marginally less powerful than PS5 at the Switch launch price would sell. I feel like sales would be through the roof and Nintendo would more than make up on software sales any hit they might take on hardware costs.

How likely is it that Switch 2 does native 16k resolution (TV, on the controller only 12k), with 50 gb ram, 10 terabytes of SSD, DLSS 7.0, all under $359.99?

Resident Evil 4 on the iPhone Pro doesn't even match the base ps4 version. DF seems to think it is 300p upscaled to 700p. Framerate is mostly stable at 30 fps.  Genuine question, given what we are seeing from the $1200 iPhone Pro on modern games, do people still think the $400 switch 2 is going to be comparable to the ps5?

https://www.eurogamer.net/digitalfoundry-2024-resident-evil-4-on-iphone-15-pro-targets-the-ps4-experience-but-doesnt-quite-hit-the-target