A new high power/small package/safe/(cheap) power source.

I.e. a cars worth of batter pack (or more) in something the size of a quarter.

One years worth of a home's energy needs in a AA form package. Compared to today, basically a limitless amount of energy. Eliminates central power - and therefore control of power world-wide. It would be geo-politically destabilizing (at least at first), make all sorts of transportation real, eliminate power generation (and use) pollutants. With cheap power comes cheap goods and cheap food. Basically a democratizing of energy.