If Visa, Mater or other credit companies adopt digital currency, it is good for all of us.
I'm not so confident in the positive outcome.
All banking and payment monopoly is based on regulation and law.
Anti money laundry law, consumer protection against fraud, .... all those buzzword are made to raise the entrance price of new player in the payment industry.
Monopoly is established.
For working in payment industry one way to kill competitor is to force partner with him and force him to respect market standard !
The problem of bitcoin is that it doesn't care about use of money. It's just a media to transfer value, whatever the aim of the transfer.
VISA and all other are all linked to TRACFIN and global survey of money transfer.
So working with them is a dangerous game.
And Bitcoin can just be killed by communication: "look we tryed to integrate bitcoin in our solution, but it appears that it cannot satisfy our security standard about ....."
Also working with those player has the side effect of loosing the little freedom of use bitcoin introduced. Those infrastructure like VISA are designed to shift the control of money from owner to them.
Using a VISA credit card means you accept that 100% of your everyday habit and use, and also wealth estimation become strategical information for VISA and partner (government and law enforcement agency).
Bitcoin was reducing the cost for alternative use of money, you don't need to create offshore company, building complex scheme for obfuscating your money usage.
Working with such partner will report the same problems in the bitcoin world.
For example, i'm always feeling self mitigate when big retailer announce they are now accepting bitcoin.
Its an easy way to build a file of bitcoin holder that you can easily transmit to gov agency.
Because they now put a name on bitcoin holder.