I’ve just merged a feature into the ac-get beta channel that I am rather keen on. It is the Plugins Feature. They allow you to extend the lib-acg runtime. This means that you can define additional package directives, and thus allow the downloading of additional resources, for example.
I plan to further enhanse this capability with more hooks for plugin developers, depending on community feedback.
The feature should be available to anyone who is Beta Testing ac-get.