As reported on twitter by @JoshDJX Cataclysm uncommon and rare gems on the PTR currently show as having "No Sale Price" and can not be sold to vendors.
I hopped on the PTR and can confirm I am seeing the same thing. It seems that lower raw gems may not be affected as raw Tigerseye and Malachite still have a vendor price. The same was true for the cut uncommon and cut rare Cataclysm gems I tested.
After Patch 4.3 you may have to cut each and every gem in order sell it to a vendor. So what if anything should you do before the patch if we have large stocks of undervalued rare and uncommon Cataclysm gems we were planning to vendor? Head past the jump for PTR prices, maths and some suggestions.