Unfortunately I think the diesel plug-in concept will only take hold after a year or more of 4 + dollar gas.
I would love to buy a 20K electric plug-in that I could drive 40 freeway miles on just the batteries.
I would probably only add liquid fuel maybe once every six months at that point, add a few solar panels on the roof not to mention without the most troubled part of the car (the transmission) the maintenance bills would go down as well I would think.
Talk about disruptive tech though, I guess gas stations could still sell a lot of coffee in the morning , but they would need to improve on that as well.