The only issue I see with this (whether card trading or electrum based) is that it if it is available to any player, it can get abused by people selling electrum (or cards) for real money... and then you end up with all the issues of money selling problems you get on a lot of MMORPG's (like WoW, etc.).
E.g. This could lead to more people trying to hack other players accounts to sell their hard earned stuff. (even just electrum)
Right now, there is little reason to do so. Since there is no way to transfer anything, there is not much to be gained.
With this feature, a person could hack into an account. Funnel all the money into a code to syphon it into an account they own. Then they could sell off the electrum (e-bay etc.) for real money. Once there is a real world money incentive, you will almost certainly see people trying to take advantage of it.
I do love the idea of making it easier for people to set up / sponsor their own tournaments, but there needs to be a safeguard in place to prevent it from being abused.