Right… Maven uses POM (Project Object Module) files which provide version and dependency information; a JSON info file would do something similar.
One thing I was wondering was whether you could actually use the Maven API directly. I had a quick look at Leiningen, which calls into Maven from Clojure; it doesn't look that hard, but it certainly isn't trivial, and would need quite a bit of support code.
Re: Jython. The real problem is that Max packages don't support JAR files, which is a truly major drawback. Joshua suggested that unpacked libraries of class files might work. I may quickly knock up an unpacker in Python or Clojure and see if that works; if so, then Jython could work inside your system. (Alternatively, your system could be extended to deal with JAR files independently, although in that case you really should be making use of Maven.)
Then again, someone might just implement native Python…