The JVM give me a few key features:
I know that a good sysadmin can manager a python app as well, and the ability to make a python wrapper around c/c++ takes us a long way as well, but the JVM is important.
I've been thinking about the JVM to support a ESB (http://mule.codehaus.org/). Do the Java bits in java, and the agile parts in python, and link them up with clean API's. Unless the overhead of the extra socket call is too much I like this better then running Jython in the JVM.
Once you have the overhead of a J2EE server I don't think scripting langs buy you that much. And I feel that you would lose a lot by trying to run a java app server in a non-J2EE environment. J2EE is complex because it helps solve complex problems, its just that not all web apps are all that complex......
the only place I can see scripting saving you anythin is in a JSP, but really you shouldn't have that much code in those things anyway. A Jython instance is not that hard to embed and work with, in fact its quite simple. I have a custom shell for Jython fairly well developed and it not that hard to manipulate the PythonInterperter via its api. Im going to assume that it will be much simpler to work with the interpreter in the runtime than playing with a socket connection, even if it is hidden behind a good API.