jetfueldrinker:
Yes, diesel fuel may wax at low temperatures (if not treated) but JETA1 is ok down to about -40C (assuming no water content)
JETA1 may cause some injection pump problems if the lubricity characteristics are not addressed (AVTUR/FSIIwould probably be ok).
Lady Heath :
There ARE a few manufacturers of GA specificic diesels - I saw at least 2 at the PFA Rally at Cranfield this year - I remember one was a very clever 2-stroke design with 2 pistons per cylinder.
It might be worth dropping the PFA a line for some info - you should find their web-site with a good search engine.
Also saw a French homebuilt (Europa style)with a Vauxhall/Opel 1.8 turbo diesel installation - quiet, clean, good endurance and a very impressive climb.
The only drawback that I could see was the reduction drive for the prop.