I have prepared a patch which allows the plugin interface to be a bit more intuitive.
It combines the spartacus/external plugins into the same interface you use to install downloaded plugins, so this is now one large list of plugins. The new list also allows to be grouped by one level of categories.
Some plugins in the list, and some spartacus plugins have been given the new "group" property so that you can play with the patch.
For the interface to load faster I have created an intermediate cache, that stores the plugin metadata and makes it retrievable easier on the interface. The upside of this is that the list of plugins is now much faster created.
This may possibly cause a lot of trouble, so do not apply this patch in a working environment. Only use it for fun and report back to me how you like it.
In a future step, the new (localized!) plugin XML metadata can be used easier on a pear.php.net like interface.
The patch can be found here: http://blog.s9y.org/uploads/plugincat.diff
UPDATE: New diff file http://blog.s9y.org/uploads/plugincat2.diff supports Template downloading via Smartacus, uhm Spartacus. :-)
UPDATE 2: New diff file http://blog.s9y.org/uploads/plugincat3.diff contains support for alternate file mirrors. The list of mirrors will hopefully be updated soon to contain some backup locations.