This field would allow you to update items in the catalog that have been labeled as unapproved or discontinued, with a specifically approved alternative. After checking out a project, what are people supposed to do with the list of items identified as unapproved or discontinued? There's no clean or intuitive way for someone to easily get those items swapped out of their project.
Everything just gets real messy, real fast, because there is no way to link that kind of information. It doesn't make sense for pricing to be the only real info that sync's, especially when there are so many other fields that can also be updated.