I don't think that they will add Ripple in the near future. They publicly stated on January 4th that they are not adding any new coins to Coinbase/GDAX.
As of the date of this statement, we have made no decision to add additional assets to either GDAX or Coinbase. Any statement to the contrary is untrue and not authorized by the company.
RE: Do you think Coinbase will add Ripple?