It's not realistic because insurance rates may go up?  Did they go up significantly in other cities that have passed similar legislation?  Assuming those rates do go up, do the lower HVAC costs make up for it for owners?  How about the extra work that roofing companies get to do?  What about the economic impacts of the manufacturers of these?  Or the positive impacts of a lower heat island effect, lower pollution, and less strain on the storm water system?