Linux is not something that handles hiDPI. X handles it, Gnome handles it, Qt handles it. Almost all of them are a bit different, and you have to take care of them separately. There are things that already work together well, e.g. X DPI detection works with Gnome 3, but if you open a Qt GUI (old Skype) then that might very well be tiny. Chrome has not worked well until recently, I don't know if they fixed it already or not.