Point of clarification: there was no prior announcement that Coinbase would support trading of BCH. In the blogpost to which you likely refer, it is made clear

Point of clarification: there was no prior announcement that Coinbase would support trading of BCH. In the blogpost to which you likely refer, it is made clear in the last two paragraphs that they would enable withdrawal of existing BCH balances but trading support would be determined at a later date [0]. This closely follows how they enabled the temporary withdrawal of Ethereum Classic after its fork in 2006 [1]. [0] https://blog.coinbase.com/update-on-bitcoin-cash-8a67a7e8dbdf https://blog.coinbase.com/update-on-bitcoin-cash-8a67a7e8dbd... [1] https://support.coinbase.com/customer/en/portal/articles/2524725-ethereum-classic-faq https://support.coinbase.com/customer/en/portal/articles/252...