THis is a great idea for getting a little cash up front but let's at least make it fair for the player.
Whatever gems you buy in BETA will be wiped when it goes live I am sure so - all purchases made in BETA should be transferred over to the live game. Not whatever is left that you didn't use but the entire purchse.
If you bought 16000 gems in BETA - you should start the game with those 16000 gems when it goes live. Otherwise, what is the incentive for purchasing in a BETA?
Just my two gems worth . . .
Abatha