The sheer volumes on coinbase and ease of using coinbase alone would be enough to spike the price of steem, of that i'm 100% sure, especially if the enable fiat to STEEM and even if they dont its still pretty easy to swop with blocktrades. We saw how ETC pumped when they were just mentioned with a listing to coinbase.

It would also help spread awareness too. I remember when coinbase purchased earn.com the sheer volume of articles and videos on the internet about it was insane. it really only be good for steem