There was a time when 320x200 graphics with 256 colors was amazing. Would 800x600 have been considered "high DPI" back then?
Or in the time were people were playing Duke Nukem 3D at 640x480 pixels, would they have considered 1920x1280 to be "high DPI"?
Windows has transitioned all the way from 640x480 in Windows 3.11 to the resolutions of today, why would there be a problem with just another step up?
What is "high" DPI today? What will it be tomorrow?
I'd say that all displays with a resolution (here I mean dpi) so high that its uncomfortable to use with current desktop programs are "High-DPI". Once the software is changed to allow arbitrary dpi scaling, there will be no barrier, so there is no low or high dpi anymore, just higher dpi. (And ultimatively, as soon as you can't see individual dots anymore, it won't make sense to increase the dpi further.)
Eventually it doesn't make sense to make denser panels because you don't see the difference anymore. This next generation of displays definitely isn't there yet, but it is "high" as in "we're getting there".
I personally can't wait until we cap out pixel density, because then we can get variable refresh rate and color accuracy back. I want my 300 PPI vbr up to 120hz 10 bit color panel monitor for $300!
However at the common "high" density used in cellphones these days, 320+ DPI or so, artifacts in non-AA fonts are still visible (not always, or to everybody, but sometimes anyway).
So, at least, there are some cases where higher-density than today could yield some benefit.
Net step would indeed be disabling anti aliasing
Also, there is the fact that you can move your face closer to the screen to look at something small. The eye can resolve over 800 ppi at 4". Finally, the fact that the eye can resolve say 300 ppi at a particular distance doesn't mean that's the best resolution for the underlying screen. If you want to render without tricks like anti-aliasing, you want to have enough resolution so that you avoid visible artifacts. E.g. imagine rendering two adjacent thin diagonal lines separated by 0.3 arc-minutes (the spatial resolution of the eye). You want enough resolution so that you can render those lines without their touching anywhere.
The transitioning all the way down from 320x200 to today was possible because the same character was always readable, even though it previously covered half of the screen.