So, in effect, the more bad things you do, and the bigger the damage you cause, the lower your insurance coverage, so the government doesn't end up in effect subsidizing villains. Also, it acts like a purely voluntary registration law - the insurance companies have to know just who they are insuring, after all! So you could opt out of registering, but if you are caught, you are liable for damages. The vast majority of non-registered supers are thus street-level people who don't do much collateral damage, but there are the occasional batman-types who work on a high level, but never register.
I really like this concept!