I think I understand where bobc's frustration is coming from. It is fragmentation. It is present in a lot of open source projects. As the code is available anybody with a minute to spare can make some kind of extension. After some time you have a system with which you can do a lot of things, but you have to set it up from various sources. Additionally some developers are not really experienced and their extensions might not be compatible with somebody else's, just because of the wrong setup of their extension.
So when you see how much effort was put in, but nobody can really make use of it, it is quite sad.
Comming to the subject at hand. Yes the solution is intended for action plugins. But hopefully we will learn something from that, and if we do and if we don't give up, it might be extended for other plugins as well (I am not certain, but I think all of the plugins are contained in the same folders, so this should be doable), so at least plugins would be covered.
To also cover footprints, symbols, templates and 3D models is beyond current KiCad python capabilities. Such a download manager would have to be accessible from Kicad launcher. And it would require cooperation from the Kicad developers. Though the idea is really good.
People like me ask what I can do now and what I can do alone as I've never really worked in a big open source project. With pcbnew python support and as I know a bit of python (but C++ scares me) I can write an action plugin and I can put a GUI on top of it. And I go and I do it.