Jamie Lokier wrote:

Why not just install .tgz or .zip files of entire binary packages, and
let the filesystem unpack the bits that are needed when they're
needed.  Some platforms (i.e. Java) do this already with .jar files
and it's quite popular.  This would extend it in a versatile way.
 

I like this notion of a plugin that would install a package if one of 
the package's executables was invoked by its name.