Also pointing out that you burn mastercoin when you trade a smart property for a smart property. Does that mean you constantly need mastercoin to trade anything? A distributed exchange is to me like creating a free market. With the fee you always bring it back to mastercoin. It almost hinders the person wanting to trade just that one smart property. Adding a extra step. If I misunderstood that blog post then disregard the last part of this post.
Instead of burning, There is a proposal to charge a fee only if the offer is filled.
Ex.
Alice offers 10 xcoins for 20 ycoin. It is not filled, no fee is charged.
Bob offers 20 ycoins for 10 x coins. It is filled, Bob is charged a fee ex. 1 msc and it is given to Alice.
This is to encourage filling up the meta dex order book.