I can understand the frustration seeing BCC skyrocket causes Coinbase users but I do not think any lawsuit can hold up.
1) Coinbase made it a point to notify its user base of its decision to not support BCC and to allow any user enough time to pull their BTC out.
2) Anyone who signs up for an account on Coinbase agrees to the terms and conditions of Coinbase which state, "The Hosted Digital Currency Wallet services are available only in connection with those Digital Currencies that Coinbase, in its sole discretion, decides to support."
3) For those frustrated with it taking a whole day for their funds to be transferred, Coinbase also states, "it may be necessary for Coinbase to retrieve certain information from offline storage in order to facilitate a Digital Currency Transaction in accordance with your instructions, which may delay the initiation or crediting of such Digital Currency Transaction for 48 hours or more. You acknowledge and agree that a Digital Currency Transaction facilitated by Coinbase may be delayed." in their terms and conditions.