I understand crypto can work with micro transactions but it's unclear to me that usd would not work. I know it's expensive through the credit card model but surely some version of mobile could be adopted.
You could use a blockchain to make payments denominated in USD. (e.g. Ripple) Previous to blockchains it was generally thought that micropayment protocols were expensive: after Bitcoin, people stopped caring about what they cost.<p>Blockchain or not, it is hard to get the costs down. Some of the problems of the credit card model (fraud) never go away.