Diesel-electric hybrid cars already exist, just not offered here. Citroen most notably, but also VW getting into it. Hybrid electric systems are expensive, diesel engines are expensive. Combine the two and the market just is not there in the US, or so goes the reasoning.
Mercedes could probably pull it off if they cared to do so, being already perceived as a premium luxury marque, the cost penalty wouldn’t be quite such a game killer. It would have to be a status symbol even among Mercedes and competing vehicles, though. The ground that Tesla has staked out, essentially.
Maybe Letourneau will enter the car market. they have been building diesel-electrics for years.
Do the diesel-electric hybrids have a large (and expensive) battery? Some of the ones that found had large batteries just like the gas hybrid, so I can see that the cost would be quite high.
The diesel powered VW Jetta is about $5,500 more than the gas powered version. So it seems to me that if the transmission was eliminated (replaced) by a generator (directly attached to the engine) and fed current directly to the electric motors on the wheels, the cost should be relatively low since there would be no need for the large and very expensive battery.
Maybe I am call my idea a hybrid. I am suggecting a diesel powered car that has no large battery or transmission (diesel/electric).