But you keep throwing around 300 ppi? And the 90 ppi you lament isn't that far off, depending on how far "normal viewing distance" is. I have pretty much confirmed that most computer desks are roughly 25" in depth. Obviously the monitor sits in a bit, generally. However, you also don't normally sit right up to the edge of the desk either. I'd guess most of us have the monitor around arms distance away, and the average long sleeve is 32". So that comes out to roughly 105 ppi as a guess. I'm not saying we can't do better with our desktop monitors, I'm just saying you may be looking for unreasonable ppi for desktop monitor use.
Also, like I pointed out the problem isn't with packing pixels in. The problem is that the large you make the screen while maintaining the same ppi the more overall pixels you're going to have to push to the display, and that makes it much more difficult to interface with. Making a 24" 300 ppi display wouldn't be hard, but making it actually work is a different matter all together.