How would this be enforced among the pitbull population?
This is a good question, since not all cops or even ASPCA employees can identify a pit from another breed. However, there are those pockets of areas of known pitbull fighting and breeding, where the cops are aware of the dogs and the owners. It's just a matter of confiscating the animals to shut it down. This is how this law will help. All it would require is a warrant to enter the property in order to scan the dogs.
No chips, the dogs go with the cops. So in this way there's no need to try to actually bust a fight or wait for a neglect case.

Also, if a particular pitbull is being a nuisance or threat in a neighborhood b/c of a negligent owner, same deal. There's no need to wait for the dog to actually attack someone.