I thought we did have those already..
We would have had a lot more now, and for cheaper, if the emission regulations were relaxed. State holdouts like CA were the places that stopped official DOT from allowing diesels into the country until they ran complicated and expensive emission-cutting technologies, and only now are slowly getting into the market. Even Honda has a great diesel but it is unlikely we will see it over here because to be DOT supported and therefore can legally be bought and sold in the US, it has to pass all 50 state's regulations. The Honda diesel, named one of the best powerplants of the year when it was introduced, does not meet CA standards.
Nor Subaru's diesel.