I agree. It was a nutty idea in its implementation and carried out on a whim. However 'split in half' probably was a poor choice of words.
But if one were to create a bunch dummy categories (a reservation pool) one could simply unpublish them and then re-work them as need. Anything added after could then be considered <some new use> and dealt with using some logic. "Show this range as normal categories, show this range as <some new use>".
Still fraught with traps- but mostly just harmless ones however requiring many logic changes in the code where they might pop up.
After playing with Fabrik a bit last night it is clearly a tool for the non programer that can greatly extend the presentation potential for JEM without having to bother developers, hack at core files, or come up with some other crazy idea

With 4 little lines of code on the core I have already seamlessly embed a full extended form (component in a component) in the JEM front end admin (with proper ACL) and access to my new tables- jem_cust_venue_categories and jem_cust_cats_venue_relations.
Venue categories for me. WhooHoo!