There's always a chance but I think you'd need to consider the popularity and use case of a coin before coinbase would consider listing it.
The likelihood is that a coin such as Ripple or something similar will be listed. Steem is still a little bit of a dark horse to many since Dan doesn't have a great reputation in the crypto world. Bitshares and EOS still have a little bit of a smelly reputation with many. And a currency that can be earned via proof of brain may not be looked upon as favourably as other such as Ripple et al.
I don't think Steem needs to be listed on coinbase for it to be heavily utilised though. We already have such an awesome community here, and it is growing by the day. And as SMTs come online we'll only see a greater level of adoption of Steem with an expanding use case to boot.
So, I guess my final point is don't worry about where Steem will be listed. The best we can hope for is that the community continues to strengthen and that more uses for Steem are created by our ever expanding community.
As many people say, Steem on!