Check the news - coinbase announced the may be adding 5 new tokens!
The candidates are:
- Cardano (ADA)
- Zcash (ZEC)
- Basic Attention Token (BAT)
- Stellar Lumens (XLM)
- 0x (ZRX)
The most interesting choice here is Cardano, not becau5i find it unfit, but rather because it's a huge vote of confidence for Cardano. If you're not familiar with this coin, it has roots in academic research and aims to create an optimal computation layer (like ethereum's smart contracts) as well as an optimal transaction layer secured by true proof-of-stake.
Cardano's solution to proof-of-stake is called ouroboros, and differs from delegated proof-of-stake we've seen, for example here on steemit or powering EOS. Coindesk recently discussed their proof-of-stake in more detail here.
Read more about coinbase potentially listing these 5 coins here