You must be avoiding quite a few games, then. Because sub-native res isn't exactly uncommon on any console. And the AA makes the resolution difference mostly moot anyway.
Subnative resolution, though not extremely rare on PS4, is nowhere near common either. A quick perusal of publicly available data suggests it's under 10%, which I would definitely call "uncommon".
The AA doesn't even come close to making the difference moot. Digital Foundry didn't claim that, and what they did claim--the AA gives results that "really aren't bad"--isn't comparative at all, just a subjective assessment of the AA in and of itself.
Its a third of the PS4 resolution, on a handheld. So you've got a 6 inch screen sporting 1/3 the resolution of something that's going to be displayed on a screen 7+ times the size, which one is more brutal?
PPI and resolution aren't the only things that play into perceptual acuity. Distance from the screen matters a lot, and TV users sit many feet away from their large screens (between 6 and 15 feet is typical). Handheld Switch will never get more than 18 inches from the eyes (arms' length), and will typically be much closer. This can negate much of the pixel density advantage Nintendo's machine has.
Which skirts around the much bigger point: because of the low rendering resolution, Switch effectively doesn't actually use its high PPI for
Snake Pass. For every 9-pixel block, there are only 4 pixels of data.
I really don't think its blurry as a result of of being lower resolution. The pixels per inch are still higher than anyone will view the PS4 version in on a TV. So obviously something with the AA is causing that blurr.
Again, PPI is not all that matters and Switch isn't utilizing it anyway. In addition, while I'm not conversant with the details of Unreal Engine 4's TAA implementation, I highly doubt it would soften overall IQ to such an extent. That's just not what modern methods do. On the other hand, the universal, uniform blur of the Switch footage (and the PS4 and Xbox One footage, to a lesser extent) looks
exactly like the results of upscaling, familiar from any number of sources.