In order for them to require a helmet that is of a certain style would mean another amendment to the law. Currently the law for helmets will go into effect jan 1, 2013. The part that does delay enforcement is the rear seats that are not factory installed. Also the feet touching the floor boards have been stricken from the law. The way the law stands now any dot approved helmet will be ok.
Also my personal option is that helmets suck and so does this law. But if you are not going to be an outlaw and continue to be taxed by California and abide by this law, a helmet that covers the ears, I believe make it more unsafe. At least if you don't wear headsets, by block another sensory from you. I know when I ride my dirt bike I can't really hear what's coming up on me or someone yelling. If you have open ears on a helmet you can. But this last part is my 2 cents.