That's the trick, Visa won't do cryptocurrency payment, they will do "fiat currency" payment indexed on cryptocurrencies.

For example, you buy 0.1 BTC using euros, you then pay a merchant asking for 0.1 BTC, which he will withdraw as dollars. Noticed that neither the buyer nor the seller manipulate bitcoin. No address, no transaction on the blockchain. It shows bitcoin on your account but in reality, it was a euro to dollar transaction.

Most likely you will be able to have a bitcoin account too, but again, dollars in, dollars out. If bitcoins raises in value, you get more dollars, if it crashes, you get less, but you never get actual bitcoin.

Edit: And BTW that's the reason why most people are using cryptocurrency for, as an index like gold. Besides criminals, few people use it to make payments.