Coinbase has just announced that they are going to support ERC20 assets, meaning that Ethereum tokens would be added to GDAX and later on possibly to Coinbase.
The GDAX team will wait for additional regulatory clarity before deciding which ERC20 assets to support on GDAX. Support for ERC20 will give a path to enabling the safe recovery of customer ERC20 assets inadvertently sent to GDAX Ethereum addresses.
Coinbase will only list assets after they are listed on GDAX. After evaluating factors such as liquidity, price stability, and other market health metrics any ERC20 asset added to GDAX may be added to the Coinbase platform. But listing on GDAX does not guarantee listing on Coinbase.
Additionally, like GDAX, support for ERC20 will give a path to enabling the safe recovery customer ERC20 assets inadvertently sent to Coinbase Ethereum addresses.