That's actually a different kind of scaling. The one at issue here is closer to cmd-plus/minus on desktop browsers, or two-finger zooming on phones. It's hard to make that look good unless you only have simple flat UIs like the one on this website.
They did make another attempt at it for apps with Dynamic Type though.
User scale and device scale are combined into one scale factor as far as the layout / rendering engine is concerned and thus are solved in the same way.
I'm certain that web style scaling is what the vast majority of desktop users actually want from fractional desktop scaling.
Thinking that two finger zooming style scaling is the goal is probably the result of misguided design-centric thinking instead of user-centric thinking.