Coinbase does not have a "there can only be one" mentality like a few other Bitcoin companies. But it won't be beneficial for me to push Litecoin until Coinbase is ready. But given that they hired me, it's pretty much a given that I will make it happen eventually. Here's some things people need to keep in mind to understand why it's not happening today:
1) Lack of exchanges (LTC/USD and LTC/BTC) that have volume and trustworthy. Bitcoin has BitStamp, but Litecoin only has BTC-e. BTC-e is anonymous, so it would be too risky for Coinbase to put a lot of money with them. The other LTC exchanges are all too small.
2) Adding Litecoin may confuse users. Coinbase's goal is to make Bitcoin (well cryptocurrency) easy for the average user. It's already hard enough to make Bitcoin easy. Adding Litecoin would confuse the average user. So it will take some time for Bitcoin/Litecoin to go mainstream. Take gold/silver as an example. If a gold exchange today announces that they will trade silver also, their customers would not think WTF is silver. But most Coinbase users would think that about Litecoin. Having BTCChina and Huobi and all these other exchanges start trading Litecoin will help with this.
3) Implementing Litecoin will take resources away from all the other amazing stuff we are working on right now. Coinbase's engineering team is tiny, but we are growing. So it's a balance to figure out what's the best bang for the buck things we work on next.
So the risk/reward for adding Litecoin does not make sense right now. Things are looking good though with all these good Litecoin news. When the time comes, you can bet I will bring this topic up.