TSR gets rid of all the shimmering and jaggies that's for sure, but c'mon, you can easily tell the final image is way below 4K. It's like watching a 1080p blu-ray move instead of UHD one - sure there are no image artifacts in both, but only the UHD one gives you that sharpness and all the tiny details.
Upscaling is obviously the direction the games are taking, the tech gets better and better each year, but a software solution used from as low as 1080p can go only so far. The engine obviousy needs a lot of work seeing how even with such upscaling the demo runs in the 20s most of the time.
Im not saying 1080p will look like 4K. (especially to nerds)
If you read my post i stated if TSR bumps 1080p to 1440p
Asking someone if the image(in motion) is 1440p or 1080p the majority of people wouldnt be able to tell its 1080p vs a native 1440p
Assuming the games internal is 1440 - 1800p and bumps up to 4K.
You would again find that most people wont be able to tell the game is at a lower resolution.
To summarize
TSR 1080 -> 1440p vs 1440p (nobody would be able to really tell which is which)
TSR 1440 -> 1800p vs 1800p (Again hard to tell)
TSR 1800 -> 2160p vs 2160p (Most people wouldnt be able to tell).
Even today the vast majority of my IRL friends who are basically a good representation of what gaming at large is (most gamers arent on forums or even know what digitalfoundry is) 1440p might as well be 4K for them....even before upscaling the image.
The Matrix demo for them was as good as 4K native even if at best it was reaching a TSR bumped 1620p and theyve seen native 4K before.
When you are trying to impress the majority NOT DF thread lurkers getting a TSR bump close enough to 4K is more than enough.
Which is why this demo still impressed even with its "low" resolution.