What about the idea to store all the plugins and behaviors similar rexrainbow does it already now, and describe them only on a (dynamic) website.
With SVN-clients it should be possible only checking updates in specific folders(=foldernames=the installed plugin-names) in this complete repository. Perhaps anybody knows/finds a very simple and configurable svn-client or something better.
This should be easier possible or not? Sure, the png-Images but this is another problem..