The problem is running GUI code as root as it’s never been vetted for that. What you want, effectively, is to have EDITOR variable of your session set to kate and open system files using sudoedit. I’m a terminal guy myself, so this exact thing is enough for me. Having said that - I’m sure someone will chime in with a plugin/addon/extension/etc that adds this to the right click context for what I assume is KDE. Or you can try looking for that om your favourite search engine.