Diesel + Hybrid would make a good match technologically, but not financially. Traditionally diesels are a bit slow "off the start" and an electric motor could definitely fill in that gap nicely. As it is, you often see turbos on diesels being used to remedy the slowness off the line.

Cost is the big issue because a diesel engine adds a couple thousand (or more) dollars to the production cost of a car (vs. a gasoline engine). Add the cost of adding a hybrid powertrain, which is typically a couple of thousand dollars, and then you are looking at a starting MSRP that is at least 4 grand more than a regular gasoline version car. This is too much for most people to justify, especially on a smaller or less expensive car. If the diesel + hybrid one-two punch does appear in the marketplace, it will probably be on a vehicle with a high MSRP to start with or on a premium brand where the price markup is substantial adn the 4K+ difference is not so noticeable compared to the overall price of the car.

I hope this is helpful info for you.

Regards,
Neil