The good news is it is very unlikely to even make it to a vote. Everything I've read says most of the officials are not going along with this. That said it is important for the residents of San Francisco to be proactive about this and let their voices be heard.
The IBC convention is in San Francisco this year. While I doubt they'll do anything in regards to this matter I wish they would make some public comment regarding this proposal for the media during the convention.
Legislation is not going to solve the problem. BYB'ers are still going to breed, un-educated people are still going to let their dogs wander around unaltered, people are still going to get pets on a whim. The only way to change the issue is for society as a whole to change its views on animals. Its sad to say that even in our pet loving society people still view animals as disposable commodities. Get a puppy, puppy starts mouthing, dump the puppy instead of taking the time to teach him. Cycle continues.
Pet stores need to find a way to sell quality, cared for animals, do their best to educate their customers on proper husbandry, but still keep up with their bottom line. Most companies care less about the product their selling or the people that work for or buy from them than they do about their profits.
Puppy/animal mills need to be cut down on while not interfering with ethical breeders, because despite popular belief dogs, cats, hamsters, fish, snakes can all be bred ethically. Dogs and cats bred by ethical breeders never end up in shelters because they're strict in their contracts and even microchip their animals with their information.