FWIW, it appears that there are a number of diesel hybrid concept cars. Two notable ones are a 70 MPG VW Rabbit/Golf and a 40 MPG BMW X-5.

http://money.cnn.com/2008/03/06/auto...ion=2008030715

http://www.detnews.com/apps/pbcs.dll...TO01/803040452

The CNN article is an interesting read. Can't tell if the author dislikes diesels, hybrids or both. He seems to point out the negatives for each.