I know there has been some interest in polymorphic components. Personally I would find such a feature very compelling because it could be used to elegantly implement the Strategy pattern. Stateful strategy components would be very flexible.

I'm a huge fan of the Strategy pattern and use it all the time for static strategies and then map the strategy as a custom user type. I would also like to add stateful strategies that hibernate persisted for me.

Has anybody done any work in this area? How difficult would be to implement this feature within or on top of the framework?

I ran into exactly this use today, and was saddened when I had to put my Strategy objects in their own table just because polymorphic components aren't supported.

Well, maybe "saddened" is a bit strong, but it would still be a "nice to have." :)