Someone has made a ‘strong hybrid’ Mini, that is a car with an internal combustion engine that is used solely to generate electricity, and is not mechanically connected to the wheels at all. There are a number of benefits to this approach:

• The engine can be run within an efficient range – having an engine that can rev from a few hundred rpm up to several thousand inevitably compromises the efficiency of the engine. Separating the engine from any direct power need means it can run within a tight rpm band. This is inherently more efficient, and also allows secondary efficiencies (you don’t need to use much energy on balancing the engine, for example).
• You can size the engine for greater efficiency – if you have a reasonable amount of energy storage onboard you don’t need an engine that can create 200bhp on demand. Instead you pick one that very efficiently does 20hp (in this case) and just run it continuously.
• Mechanical losses in the transmission, diffs etc. are greatly reduced. Naturally some of this is counterbalanced by the inefficiencies of the conversion to electricity, but the other benefits mentioned here come for ‘free’.
• It’s inherently a modular design. If someone comes up with a better energy storage system than the battery, you plug that in. The same goes for the conventional engine, and even the in-wheel motors.
• You get to run electric-only when needed. If you’re heading into a polluted city, or even just a long tunnel, you can switch the conventional engine off and run solely on the battery, reducing local pollution when it’s needed most.

All of that, and I’ve not mentioned that you can run on electricity from the grid that has huge potential for being more environmentally friendly than a oil-burning engine.

Unfortunately I suspect this might cost a little more than a Prius for now, but there’s no reason why this couldn’t be a serious option very soon, and would provide a useful platform for the developments such as fuel cells that many people are touting.