The question posed by the original poster assumes that there has been a transition from petrol to diesel and I'm not sure that assertion is accurate. It's true that diesel-powered vehicles abound in far greater numbers today in the UK than previously but there are many reasons for that, some of which are so diminished in importance that they are no longer valid. By way of example, I cite these two facts:Will the transition from fossil fuels be similar to that from Petrol to Diesel
1) Diesel is now more expensive than petrol and
2) The advent of solid-state electronics has negated the tendency of the petrol engine to misbehave.
When it is considered that the latest, small petrol engines are hugely powerful, very frugal, quieter than their diesel equivalents and selling in increasing numbers, it's not at all clear that the diesel revolution in the UK was anything more than a passing phase. I say that because there is some evidence to suggest that the latest, small petrol engines from the VW group and the ones on offer in the Fiat group cars represent the optimal power plants for the cars that most people drive this side of the atlantic.
Mainland europeans were into diesel long before we began to consider it as suitable for private cars so we were late to the party. We will probably be caught lagging again in the movement back to petrol which is gaining momentum across mainland europe, the natural home market for most VW and Fiat group motors. Regardless of any major shift in the petrol/diesel balance, there is one glaring omission from the contributions in this thread and that is hydrogen.
Safe storage of volatile gases has always been a problem and the notion of a hydrogen-powered car has been bedeviled by that problem but we are much, much closer now to producing viable hydrogen-powered vehicles in large number than ever before. In time, I expect a hydrogen car will be where the Prius is today.
Given the idea that biofuels might be the solution has been completely debunked, to answer the original question, no; the transition will represent a sea-change in people's thinking about how we convey ourselves around the planet and how we conserve resources for future generations. The switch from petrol to diesel and the possible switch back again will pale into insignificance when compared to the abandonment of fossil fuels.
Perhaps we should all consider horses and mules again as the power source for our personal transport. Moreover, perhaps we cyclists should all be reverting to unpowered bikes of about 12Kgs and getting off and pushing when the going gets too tough?
Regards,
Indalo