Coinbase made a colossal mistake in outright ignoring BCC and will likely get sued (and lose) because of it. If I had 10 BTC on CB and missed out on the opportunity to trade or sell $6,500 worth of free BCC I just got, I'd be mad too.
They need to act quickly before it goes to court. Someone else commented that they don't even need to support trading BCC, all they have to do is provide a way for customers to withdraw their BCC, and they're in the clear.