For issues related to needing vs not-needing to dynamically create Java classes and corresponding security restrictions, it would be user-friendlier if Exception on Jython side would remain a classic-style class. We can give more input when we have sorted out the implementation of new-style classes subclassing (that's many month away :( ). Maybe the issues will become non-issues or not.
Good point. We'll be cautious.
--Guido van Rossum (home page: http://www.python.org/%7Eguido/)