I was 'edjumacated' in high school about energy, and the transformation of it from chemical to mechanical and so forth.
I've not seen any great EFFIENCY breakthoughs announced since then that would allow a certain MASS to be accelerated up to a certain SPEED for a certain COST better than GASOLINE... I do not care HOW cute the replacement package is, or how many computers it has on board.
Part of the idea is to switch to electric propulsion, since there are a variety of ways to make electricity.