I’m a merchant myself, I sell e-paper calendars. Last year I paid about 4% of my revenue for transaction costs in various shapes. That’s very roughly 20% of my margin. (!) Some of these are hidden as very bad, but non-optional, currency conversions.

The hard one here is acceptance by customers. No merchant wants to clutter their checkout page with a button that nobody understands. Or worse, have customers get trapped in a dead-end payment process.