We all have observed that cars got bigger and heavier over the last 20 years. With this gain of weight some of the progress made by building better and more fuel efficient engines got lost and actually some handling and performance also was given away.
The problem with more weight is that everything needs to be built stronger to deal with the increased weight.
Audi showed how it would be the other way around. They lightened an A5 by roughly 200 kg, by using an aluminum structure and body and carbon for some parts. Thanks to the lighter body they were able to use a smaller transmission, smaller wheels, fuel cell and brakes. At the TechDays they compared this special 4 cylinder TFSI A5 with its bigger brother the V6 A5 as built and sold today. Despite 54 HP less the lighter car accelerated as well as the V6 and the handling was much better. Fuel consumption is down to 6.2 liter per 100 km, a lot less than the V6. So, you get equivalent performance, better handling and heavily improved fuel efficiency without suffering. The only downside may be the engine sound, but as we know these things can be engineered.
And "cetero censeo ....." I am still waiting for the 950 kg super car.