> The only sensor in the scale is a weight sensor.

? Why not add a RFID reader (relatively cheap) to the scale and then add tags on the coffee bags to be able to log the consumption for multiple types?

You could even be able to identify the weight of multiple objects (tracking what's on the scale and how the weight changes when it's removed and when it's put back) on a bigger(longer?) scale.

And you could sell kits with tags that people could slap on their own containers and register multiple custom items.

I agree, "autonomous dash button" is a nice way to present it, but if it was capable of detecting what's on it, it would become more or less a "sentient dash button", way better ;)