(1) Supercapacitors are commercialized, see: http://www.mouser.com/Power/Supercapacitors/_/N-6uivw

(2) Today's supercapacitors have very poor energy density even compared to batteries. What they do have is good power density, meaning they can deliver their limited energy very fast.

(3) Boosting the energy density of supercapacitors will happen but requires many years of great strides in nanotech. Research like this, involving 3D nanostructures with enormous surface area: http://phys.org/news/2012-10-sponge-like-graphene-supercapac...