I would love to see the ability to add another layer to item types, maybe called item group. So, say you have DVD, CD, Music, etc, these things could live under the umbrella of an Item Group called maybe Audiovisual. This would enable us to put circulation rules on a group that would affect all items in the group, which would be more congruous with the kinds of policies that libraries tend to have. For instance, our policy on A/V materials is that a patron may only have 5 at a time. However, in the Circ & Fine rules, the only way we could address this was by give all of our A/V types a limit of 5 and then we have to be paying attention to each account to be sure that someone isn't taking out 5 DVD's and then 5 CD's. If there were an additional layer that could group them together, it could serve as a way to apply a limit on the whole group of item types.
I am not sure adding another level of complexity to the circulation rules would work out very well - we already have to fix lots of stuff in there :) I think maybe the itemtypes could be used differently? If you make the "itemtype" what determines your circulation rule, in your example "Audiovisual" and maybe use the collection code to differentiate between different types of audiovisuals?
*** This bug has been marked as a duplicate of bug 6685 ***