I echo Dave's feelings that the cr_keyword stuff would actually be nice to have generalized to any object rather than just content. Perhaps cr_keyword could be subtyped from an object categorization type in order to hook nicely to the CR's ability to automagically output a revision+template, perhaps that's not necessary, perhaps eventually the same capability exists for all objects, I don't know ...
Nor am I thinking you should implement this while migrating bug tracker to the CR, I'm just thinking ...
Remember that the CR/CMS used to be standalone. I would assume that cr_item was the base object type in that system and that this is why cr_keyword was originally derived from it. I suspect it got switched to derive from acs_object when the CR/CMS was stitched into ACS 4.0.