Real money wouldn't break the market. But likely the deal they made with EA is that they can't sell bfp.
Also there is no breaking the market - there is just changing the basic settings, which means the market may become more or less volatile. And currently it is actually rather volatile due to several factors - one is the amount of cards flooding in to the market with every player getting esentially what was once work 20 € per day (1 booster and 150-225 bfp). Currently my perception is that more bfp flood into the market than does cards which give rising prices.
On top of tha