Due to the fact that Mayor Nickels has merely requested (demanded) that his dept. heads come up with regulations for a gun ban on city property, not actually enacted any law or regulation an AG opinion would be premature. I am sure that the AG would wait until the actual "act" occurs before he offers an opinion.
A recent article in "Gun News" pretty much summed up Mayor Nickel's actions regarding guns as "Ready, Shoot, Aim". It is very possible that someone may whisper in his ear that he is merely "Mayor" Nickels, not "Emperor" Nickels and this action may merely fade away.