used to wonder about this too. After all, an infrastructure for MtGox codes and the like would have to be built first.
But then, Ripple came along. Ripple will enable Bitcoin derivatives and Bitcoin fractional reserve banking easily.
Ripple can already do btc derivatives.
Consider an IOU at market value. Then trade out the IOU a day later.
You have futures, forwards and contract for differences.
I welcome regulation, if the goal is fraud prevention.