Yes, they at least sound open to its usefulness. Having a well know and used payment processor like Visa may be the key to mass adoption, not necessarily just merchants. Think about it, it they will work with btc, the merchants may not even have to do anything differently! Just swipe a Visa, and select to pay in usd/btc, visa takes care of the conversion if the merchant just wants fiat! That would be revolutionary!
That's true having Visa adopt bitcoin could become the key to mass adoption, but that would make bitcoin become centralized.
You couldn't get your private key & no more anonymity. Also, it means you have to pay more fee