I notice that in some version after plasma 5.8, someone decided it should not be possible to launch Dolphin, Kate and Kwrite as root. This is very annoying as now: 1) the 'Root actions' menu for Dolphin is broken, 2) I have to use Konqueror+Sublime or Nautilus+Gedit for editing system files. I realize it's still possible to do something like 'SUDO_EDITOR=kate sudoedit file', but I don't like having to type this long sequence or having to copy the file name to a terminal, and the reason why I use tools like Dolphin and Kate in the first place is so as NOT to have to type stuff on a command line. If you think it's dangerous for some users, then at least offer the option somewhere visible for enabling launching KDE applications as root. Please don't be like GNOME. Hell, not even GNOME is forbidding users to launch Nautilus and Gedit as root.
Already tracked in Bug 387973 and Bug 387974. Keep in mind that you can now edit system files from Kate even without needing to run it or Dolphin as root. Simply open the file normally, and then when you go to save it, you will be prompted for the admin password. *** This bug has been marked as a duplicate of bug 387974 ***