Pundi X or EOS will be the next altcoin. That's really great altcoins and Coinbase will definitely look at it. This will be the altcoins that bring high volume to Coinbase and will bring a lot of transaction fee to them if they can cooperate with them. Coinbase is a safe purse and a safe trading platform so they are very picky about the altcoins. But I think EOS and Pundi X can afford it.