Lifestyles...just add cetane
If anyone can market diesel engines and diesel fuel to the American public sucessfully, it is Subaru. That's all it takes is image. In America you have to convince people that a new *thing* either enhances their lifestyle (how's about 800 miles to the tank...I could build an entire ad campaign around that alone and sell tens of thousands of cars) or gives them a lifestyle (just add cetane.)
Americans like to be told what to wear, eat, drink, drive and how to be/act/look 'cool' like no other people on Earth.
So, tell them. Show them. Give them what they want/need. I think Subaru could definitely do it. Hell, they used to be seen as an 'alternative to a truck' car maker and reinvented themselves as a 'premium sports automobile' company. Pretty impressive to me.
Only in America...Example 2: Harley Davidson positioned a leaky, crappy old tractor motor as 'the coolest of the coolest' and pulled themselves out of the dirt and into a multi-billion $ icon back in the late 80's and throughout the 90's.
So I see no reason why a company like Subaru can't position diesel engines as the 'coolest of the cool' and take this wonderful technology beyond its die-hard fanatical cult following (ahem*...that would be us) and market it on a huge scale to the grocery getters.
To sum this up, I see several companies being capable of this kind of image marketing magic: Subaru, Volvo..basically all of the 'hip' brands with youth cachet. Whichever one positions it to be 'bio friendly' is going to beat the pants off of the others. Biofuels are here to stay. They will NOT go away; they will only grow in share/usage. If several 'youth oriented' car companies bring the 'diesel lifestyle' to us, that would be great (competition always is.)