Here's another idea I had - a "Plugin Updater" plugin
In the absence of a more structured repository for plugins, the idea behind it would be that it is able to scrape the plugins sticky index to read a list of available plugins, their description, forum thread, internal name, last updated, version numbers and Calibre version required. Then a user is able to click on "Update Plugins" or whatever in Calibre and be presented with a list showing them everything available, which versions are newer than what they have installed etc. They could navigate to the forum thread, or have this plugin directly download the zip file from the thread and install the plugin for them.
I can appreciate not every user has the time to continuously come look through these forums for updates or new plugins. A button that does the work for them sounds nice. I think it would be even nicer if something like this was incorporated into Calibre and available from the Preferences->Plugins dialog, perhaps if others think it is worthwhile to develop I get it stable then see if Kovid is interested.
It has a dependency on scraping data from the index page so a bad edit could break things but it is easily remedied and not critical to Calibre operation while down. The number of user plugins today is pretty low and undoubtedly Kovid has higher priorities than putting a more tightly controlled plugin release infrastruction in place. I think this could "do the job" in the meantime and is just as easily updated should things change.
What do others think - would this be of interest as a plugin?