While I wouldn't say it looks "natural", it looks better with supersampling (than it would without SS). I've tried this on my 4K monitor, using Elite Dangerous. While upscaled 1440p (to 4K) with SS=1.5 is not as crisp as native 4K, it doesn't suffer from aliased jaggies, so in some respects, supersampled and upscaled 1440p looks better. Ideally, you'd supersample the 4K and not upscale it, but that's not an option for the Pimax 8K.
I considered getting the 5K, which would avoid the upscaling, but the pixels will be larger and more visible, than the 8K. The blending which is inherent in the 8K's upscaling will tend to introduce some fuzziness, which should make the image look more natural (like a photograph, not CGI).
Ideally, we'd be able to have native 4K for each eye, like the 8KX, so we could avoid the upscaling, but that's not really affordable for the masses (yet).