In future, can I pay in any cryptocurrency I like?

Currently there is no simple "Scan QR code and send" universal cryptocurrency solution. However, services do exist that allow simple swapping from any coin to any other coin for a fee (for example Sideshift.ai) so it is only a matter of time until a standard emerges that allows customers to pay in any cryptocurrency the customer prefers and the merchant receives any cryptocurrency the merchant prefers. At this point, the differentiator between cryptocurrencies will still be coins with a limited supply that can support the largest network of payments with the highest efficiency (lowest fees), which of course is the speciality of Bitcoin Cash.