Package: ftp.debian.org X-Debbugs-Cc: network-con...@packages.debian.org gksu has been deprecated for years. The intent of gksu is to allow running apps with elevated privileges but the recommended way to do that is for the app developer to use PolicyKit to request elevated privileges for the specific actions that need done instead of for the whole app to run as root.
For the next major stable release of Debian (codenamed Buster), the Debian GNOME team plans to default to GNOME on Wayland where gksu does not even work. gksu is unmaintained (last upload 2014) and is considered a security vulnerability. Therefore, please remove it. On behalf of the Debian GNOME team, Jeremy Bicha