If they converted Gems into a cryptocurrency, it could be bought and sold on exchanges.  A coin would be called a Bitland.

Bitlands would no longer be on sale on the site, but could only be available to members at the rate of one for each (non consecutive) thirty days the member signed in.

All coins would come into existence up front, which Bitlanders would own, and hold in reserve, but could sell on the exchanges for bitcoin.  

Bitlands would be transferable on site between, and among, members...