Currently starting a chat from the contact applet takes a double click, which is neither intuitive for a KDE user nor efficient. Since starting chats is the applet's main purpose, it should be done with a single click anywhere on a contact.
Given we had this discussion for the main contact list for this exact reason and the outcome was "no, sorry", I'm quite sure it's the same with the plasmoid. At least for the time being. But since we need to provide more actions for it, like starting audio/video calls etc, we might come up with different UI in the end, which will feature single-click-buttons. *** This bug has been marked as a duplicate of bug 282361 ***