So what happens when you make a bad trade and you're left with less than what you owe the exchange?
How would the exchange cover the trades if not enough people were depositing?
You can't owe less than 5%. In my idea, the 5% comes out of whatever left that you have to withdraw. Whoever profited from your bad trades will pay whatever you didn't.
I don't understand your last question.
Yeah sorry I was a bit tired and confused when I read your initial post. I actually think it's a great idea from a speculator's perspective, as long as there's enough trading going on.