Hey,
Didnt S1914 have that already? I dont remember specifically when but when they added planes in the game and option to pick a nation yourself, you had to spend goldmarks to join such a game.
There is an option to have your round be a gold round, which requires people to pay 5,000 GM to join, but there is currently no option to have no gold use within the round itself which is what the original poster is suggesting.