Kate and KWrite give a persmisions error if attempting to read a file that is only readable by root. Attempting to sudoedit does not work as sudoedit thinks kate/kwrite has quite without making changes. Therefore there is currently no way to edit such files with kate. This does not apply if the file is read only for current user but writable as root. In this case kate/kwrite will prompt for escalated permissions via polkit.
Valid wish, patches welcome.
We have now polkit integration that handles that. *** This bug has been marked as a duplicate of bug 337641 ***