Many stores are already switching to cash registers with displays for the customer, at least in the Netherlands, so things like this could easily be integrated into existing POS platforms.

This seems like a great solution for smaller stores, but larger stores or chains that use custom POS platforms would benefit a lot from a standardized 'POS API' (as opposed to the usual Bitcoin API) that also allows for communication with a remote Bitcoin client (which will be the case in a store with multiple payment terminals/counters, where everything has to be handled by one central 'cash register server'), and that can be used without a GUI frontend - effectively making it very easy to implement Bitcoin into an existing POS solution without any knowledge about the underlying system.