Honestly, I think its a pretty good idea (from the merchant's point of view) but what about the buyer...
...especially those that don't understand the blockchain, they would want to see other merchants using this system where they can buy other stuff using steem else they would feel like you are offering them something that can only be used in your shop.
All am saying is that for this to work we need a community of merchants to flood the markets/streets so that buyers can see other alternatives to use steem.
-Just my two cents-