I think one of the problems comes from the fact that big players affect the game. So if say, Citi launches a new algorithm that does some new crazy thing, which

I think one of the problems comes from the fact that big players affect the game. So if say, Citi launches a new algorithm that does some new crazy thing, which turns out to trigger random issues or unexpected responses in other algorithms -- such a thing could make lots of people other than citi a pile of money. Are those people really going to want Citi to test it too well? Another, real concern with such a shadow market, where say everyone is running their algorithms (to prevent the above scenario), is that i could test "a buggy version" and find holes and odd behaviors of my competetors for free, since it is all play money.