have I messed up or missed something?
------ [Desktop Entry] Encoding=UTF-8 Keywords= Name=Now Dock Type=Service NoDisplay=true X-KDE-ServiceTypes=Plasma/Applet,Plasma/Containment X-Plasma-API=declarativeappletscript X-Plasma-MainScript=ui/main.qml X-Plasma-ContainmentType=Panel ------
a panel is a plasmoid, just change the metadata.desktop accordingly and it should popup in add panels. after that works, then you should make it correctly manage adding, and layouting plasmoids in it, but that's another story