Bittrex–another US-based exchange lists ADA but Coinbase has not. Ever wonder why? Both exchanges are in the same jurisdiction, but Bittrex has no problem listing ADA based on the counsel they get from their lawyers.
Are they too aggressive? Maybe. Or maybe they just get better legal advice.
The fact is there is a precedent in the US of listing ADA. I am thinking Coinbase might just go ahead and list ADA without waiting for decentralization.