The gas mining mechanic would almost certainly be OP and goes completely against the way that the Zerg is setup. It's easier for zerg to expand, but it's also more difficult to build an economy. Building drones takes away from being able to build other units, and creating a new building requires another drone that could be mining. Having the ability to instantly gather as much gas as you want would completely undo all of this. It would practically ensure that Zerg would mutalisk rush every game. With multiple queens it would be easy to gather as much gas as you want instantly.