The overwhelming majority of the low-DPI external displays at this point are 24-27 1080p

Most high-DPI displays are simply the same thing with exactly twice the density.

We settled on putting exactly twice as many pixels in the same panels because it facilitates integer scaling

That doesn't gel with my experience, 1080p was the de-facto resolution for 24" monitors but 27" monitors were nearly always 1440p, and switching from 27" 1440p to 27" 4K requires a fractional 150% scale to maintain the same effective area.

To maintain a clean 200% scale you need a 27" 5K panel instead, which do exist but are vastly more expensive than 4K ones and perform worse in aspects other than pixel density, so they're not very popular.