diesel cars are not the huge financial advantage they claim to be, the same as in aviation.
A diesel is vastly more expensive to purchase and diesel fuel costs around 20-25c more per litre. A diesel car has no advantage whatsoever in short-trip city operation.
Firstly, you need to recognise that Australian diesel pricing is different than most of the rest of the world. The economics of diesels are different in Europe.
10 - 15 years ago, most automotive engine development effort went into diesel engines. Now its small capacity turbocharged / supercharged petrol engines. The current belief is that petrol engines can be made more efficient than diesel.
There is even development work going on at the moment with compression ignition
petrol engines.
A lot of the initial advantage of diesel was due to emissions legislation. But now that emissions regulations have been brought in to apply to diesels a lot of that advantage has eroded.
A common feature of all the new technologies is high levels of computer control. I really struggle seeing that being accepted by aviation regulators.
Australia is not getting the best of the new automotive engines. Partly because we have no policies to promote low emissions / efficient engines (eg registration & tax incentives) and partly because we are nearly alone in the world in not having a roadmap for future fuels. So, the car companies have no certainty of direction so we tend to get "lowest common denominator"engines.
Have a look at the International Engine of the year awards if you want to see some really interesting technology.
My bet is that in 10 years we'll see less automotive diesel engines, not more.