Do you think there would ever be a possibility of being able to stack cut gems? With over a hundred new gem patterns from rep, vendors, and instance drops, I can foresee the massive amount of space used in guild banks and personal bag space to keep these organized (to sell and/or distribute). Not to mention the amount of space inscriptions will take as well.
On live, I have 2 of our guild tabs dedicated solely for gem exchange, which could easily be consolidated into one tab if they were to stack.
They could stack like armor kits, but have them manually separate one to insert into a piece of armor. Inserting a stack of say 20 would just give an error saying that you can only fit one gem in that slot.