So, it's totally impossible to impose some level of deterrence on future Wall Streeters, right? How can the government write rules ahead of time that will prevent firms from engaging in dubious behavior that hasn't been dreamed up yet?
Fortunately, there's another form of deterrence. As Voltaire said after the British navy messed up and lost the island of Malta to the French: The English like to shoot an admiral now and then to encourage the others. We can encourage future banksters by what we do to the old banksters.
Now, shooting is probably a little much, but why not imprison a few 8-figure per year bank officers? That will put a little fear in future banksters. That will make them cautious about exploiting loopholes they find in regulations You may say, but that's the problem, they didn't violate any laws. And I say, I've watched Law & Order. There are a lot of laws out there. Creative prosecutors can improvise. I've seen the feds put Martha Stewart in prison even a after they found out that she was innocent of what they started investigating her for. And Martha Stewart didn't lose a trillion dollars of the public's money.