Let me ask a question, would the files that need to be tweaked to support this in this zip?
cbplug_int_cbsubscontent.zip
We're looking into this now to see if it's possible to tweak a few files to support this functionality. Our challenge is we have a site with 77,000 articles, growing by 1000 a month (medical journal site) and in the past, the editors posted articles twice to have them in two categories and CW Multi-cats seemed like the fix. Well, we know as do most that when you install another addon that monkeys with core features, it breaks something else and thats what happened here and now we need to get some code customized to get this working since it's so important for cross posting.
The reason for multi-categories is menu navigation. Thats the bane of Joomla's existence is if you can navigate via menus, then it's easy to organize content.