They are NOT adding support for these coins. They do not claim they will allow you to buy/sell the Bitcoin forks. The statement simply says they will allow users to withdraw forked coins, something they should have done a long time ago.
It simply says they are not supporting it right now but to adding the new assets due to the a lot of demands to request new assets to be listed on the coinbase platform still on the analyzation and consideration.
I guess they said that the assets must comply with DAF to be listed on the coinbase platform. I think that coinbase never supporting bitcoin fork because there is no utiliuty usage on there.