This actually sounds very similar to the package manager we're working on for Narwhal (http://narwhaljs.org/), currently called "Tusk". It has virtualenv-style environments, dependency resolution, installation from git repos or plain HTTP servers.

Perhaps we could collaborate to make a language-agnostic package management "standard". We can of course have implementations in our languages of choice, but things like the .rip file format, directory structure, etc could be standardized.