Hmmm...what about a coffe machine, that would have a plug for a HW wallet to be plugged in (and a qr scanner) and a network of coffee machines that would accept a coffee token that would be storred on a ledger or trezor or whatever, for a user to buy coffee
you mean like pre paid for coffee?
As a general idea it's a good one, but when you start looking into details many problems will show up on the part when paying people to refill it.
For example, how would you make sure the user did put water and not mess up with the sensors? even if you completely seal the machine in a secure way, how would you make sure the user did put good clean water? same would go when refilling all other ingredients.
Also, consider the network delay and fees, you'll need to use cryptos that have near instant confirmations so the user won't have to wait long for the coffee.
Finally, consider the price fluctuation, whoever sets up the machine will have to accept such risk unless they're believers of the coin.
I was thinking these problems and I think that first the architecture of the machine could be secure and not letting anyone to mess with the sensors.
Additionally it could have a system that allows only some people to refill them and that people should lock some coins in the front.
And there is a system that It could have a review system which when you pay for your coffee you say if you like it or not.If you dont like it and other for example 2 people dont like the coffee the person who did the refill lose his money.
If for example this system build on EOS the delay could be very small and the fees too.
The volatility problem I think it could me less important in the next years when we have cryptos backed by gold or the stable coin.
If you have ready this project before the time that the cryptos become more stable you can implement this in any kind of crypto.