Engineering360: "Where does the internal combustion engine go from here?"

The mass and volume fractions of the ICE can be greatly reduced in hybrid vehicles by averaging power output of the ICE over the entire transport cycle. For a super high-performance hybrid vehicle, the storage capacity for reasonable grading ability, extreme acceleration, and regeneration should not have to exceed the energy equivalent of about four accelerations to cruise velocity. For flat land efficiency the storage device should not have to capacitate more than about one equivalent acceleration to cruise. These relatively small storage requirements are well suited to the high-power densities of super capacitors, which because of their nature, can greatly increase regenerative efficiency.
An efficient hybrid would have a significantly lower carbon footprint than EVs charged with fossil fuel generated electricity.
A properly designed ICE-Electric hybrid vehicle could eliminate all mechanical coupling in the drive train by using the power shaft of the ICE as the alternator rotor when wheel-hub integrated motors are used to apply tractive effort. Such a design could integrate all wheel independent no slip technology where acceleration and regeneration would be limited only by road to wheel adhesion.