"all that is required for cold weather is to ensure the intake doesn't get blocked by snow!"
And some form of pre-heat for the fuel - diesel fuel gets very sludgy as the mercury heads for 0.
Wiksch in Northampton are going through the process of certification for their diesel - an engine designed from the bottom up for aviation. They have it flying (with a datalogging system) in several non-CofA kits.
And the Mercedes A class diesel has been converted and is running in several production planes in Europe. Both these engines make use of alloys to reduce the inherent weight that has previously made diesels useless for light aviation.
Mark Wilksch (ex-Cosworth, decent Aussie) was at Aerofair this year - and is desperately keen for Frank to let him put one in a Robinson.
What will make it happen quicker:
(a) the predicted end of 100LL: refineries are struggling to justify it. Demand has slackened off in the USA - but more dramatically in the UK.
(b) USA "gas" prices to reach $2.50 - $3 a gallon.