If a plug-in declares an id among the properties of ApplicationPlugin.properties (which is unfortunately not the case for the plug-in you wrote), Sweet Home 3D proposes to describe a new version of a plug-in (or a library) with an update XML element that respects the following DTD.
To ensure the end users receive this information, the update XML element will have to be integrated to SweetHome3DUpdates.xml hosted on sweethome3d.com web server. It's the file that is read at program launch when a user has Internet access to sweethome3d.com and the Check updates at program launch option is selected in the preferences pane. At the moment, editing SweetHome3DUpdates.xml can only be made by the webmaster of sweethome3d.com, i.e. me. [;)]
Hope you'll understand that I'll accept to edit that file only for very important udpates.