[dom0]

"Fractional scaling" (I assume you mean e.g. 160 DPI instead of 200 DPI) is no problem even with the older KDE version from F23, just a bit finicky to get started up - but when it runs, it works. Gtk on the other hand seems (seemed? - I don't bother to check regularly) to be stuck at 100 %, 200 %, 300 %, ...

[bwat49]

With gnome 3 you can install gnome tweak tool and just set the text scaling to 120-130%. Works very well on my 13 inch 1080p display

[symlinkk]

That doesn't scale the UI. And it doesn't even scale the text for many third party apps like Sublime Text, Firefox, and IntelliJ. Windows handles this perfectly.