Integrating with the fridge itself I think is a losing game. But I think a personal inventory system would find a market. Just have one of those grocery store guns tied to an app that inventories your fridge and pantry, estimates expiration times, and has a little switch to switch between adding to inventory and adding to list. I think the killer feature would be speed though. It has to work in milliseconds and be completely seamless for it to be worth the effort.