Ok, so we know that one day we will run out of petrol, and we also know that racing improves the breed, so why not open the rules up to allow hybrids and diesels to compete too. I see it working like this:
Under the new rules we only have 2.4L V8s but if a manufacturer is prepared to take a capacity cut to say a 2L V6 then they can run electric motors in the front wheels to make a 4WD hybrid car. Or to counteract the performance loss inherent in diesel a 4L V8 or 2.5L turbo with a maximum boost limit could make it a lot more intersting.
Heres the trick though, a manufacturer is only allowed to use the technology if they have a road car that also uses something relating to it. This means that Ferarri are stuck with a petrol as this is all they do, while Honda and Toyota can build hybrids, BMW, renault, Merc, and Ford (Jag) can have diesels.
Then we would see the technology moving in new directions and it would be very interesting to see the BMW diesel leading the Honda Hybrid from the Ferarri Petrol 2.4