Maybe there could be a new cooling system for smartphones and tablets that would use liquid cooling to prevent overheating. That way you could mine all day long and never have to worry about your device getting hot.
Above all this, I was thinking of a system where you can mine coins by each step you make. Similar to the pedometer feature on the 3DS on which you earned some "play coins" at a rate of one per 100 steps measured by the built in pedometer. Take a look at this here:
http://www.ign.com/wikis/nintendo-3ds/Play_CoinsThat would be awesome