After a fresh install of openSUSE 42.1, I tried to open kate via the Kate Sessions plasma addon. Nothing happend. I found out that kate is not installed. Expected: display a message that kate must be installed in order to use the Kate Sessions addon.
This is a downstream packaging issue. I use Gentoo and installing kate installs both the kate executable and the kate sessions plasmoid and it works like it it supposed to when both are installed (Requires addons use flag). It is not possible to install the plasmoid without kate.