The item itself is pretty generic... it adds a gem slot to your waist item. It seems like it should be usable on Cata gear. (The tooltip says "Item Level 80" but not *Requires* Item Level 80... so I assume there is no gear level restriction.)
However, as players move on to the Cata zones, and no one is routinely gathering the mats required to make these items, it seems like their cost is going to skyrocket. I have a blacksmith, and will farm the mats and craft them myself if needed, but I was curious as to whether this is something Blizz intends to happen?
(Please note that I have not seen a full blacksmithing recipe list for Cata... if there is a Cata version of the belt buckles planned, I have not seen it.)