The point isn't to have more pixels, it's to have more detailed pixels. You use scaling to get whatever display size you want.
4k 27" with 2x scaling is effectively the same size as 1080p 27". But one looks like absolute crap, the other is reasonably sharp and detailed. Text is much better with higher PPI. And 4k27" is just 160 PPI, the 6k 32" monitors are 220 PPI so text is very crisp.
I don't know about other OSs, but fractional scaling "just works" on KDE Linux. The size of displayed content has nothing to do with the pixels you have. You control the physical screen size (inches) and scale factor to get the content size you want, and you buy as many pixels as you can afford to get good quality at that size. There's a parent comment on this submission talking about how his 8k 32" monitor is visibly better than 6k 32" for text sharpness; TFA says the same thing. You really want as many pixels as you can afford to buy.
Of course, the minimum (densest) content size you can use is constrained by PPI, low PPI won't be able to display very small content.