The addition of ERC-20 tokens to Coinbase is very exciting news as it opens to a world of possibilities and also engages one of the most active exchanges into new territory. It also has the potential to clarify some regulation as they seek guidance to ensure adequate due diligence listing assets that are not considered securities.
I tend to think the obvious asset to look at for possible listing is EOS given the way it has been structured. However, EOS has not wanted to open to US investors and they are also a short time away to converting their tokens. Same goes for ICX as they convert. The only other ones I could think about is OmiseGo and Vechain. Those have pretty good use cases for utility and depart from securities. Others to consider would be decentralized exchanges but would not think Coinbase is open to listing competitors.