What will Coinbase do if there is a contentious hard-fork of the Ethereum chain and different USDC supporting exchanges decide to follow different forks?
In this case, the issuer of USDC, Circle, would be the one to decide which fork of Ethereum to support. It's not like USDC the ERC20 token is worth anything without Circle's backing.
This is a hard question. I don't have an answer for you, but if a situation like this arises, we'll be sure to clearly communicate our thought and decision process to our customers. Thanks for asking!