There's at least one company lurking to offer a Prius Diesel conversion, while retaining the HSD system.
http://dieseltoys.com/pricing-2/toyo...s/prius-diesel
BTW, to manage the automatic shut-off into a Diesel doesn't seem to be so hard. Ceramic glowplugs can lead to a more efficient pre-heating, and among others are already available in the Mazda SkyActiv-D engine which is usually available with the start-stop system, composite-material valve covers and oil sumps (just like the ones used in the Detroit Diesel Series 60) retain more heat into the engine, and there are also hybrid heavy-duty vehicles such as trucks and buses in Europe, and even in Brazil, which feature a driveline layout quite similar to the Prius...