Well, vending machines have been largely unchanged for several years. Last major change of which I am aware was the default addition of a bill scanner - quite some time ago.

however, US Treasury is now actively considering changing our coinage. Seems it costs about a dime to manufacture a nickel - just as an example. They're considering smaller, they're considering different metals, they're considering... I dunno what else.

So here's the thing: If our coinage is changed, every vending machine in the USA will need to be retrofitted for the new coinage. If that happens, it's game on for any and all sundry changes to the money mechanisms.

This might be a good opportunity for bitcoin.