Yes, he also mentioned this at his talk at the R.A.S. (London). Diesel helicopters will come, particularly with the rate of development at Austra Engine.
Helicopters in the short term have to be designed around the current fleet of heavy Avtur JP8 burning diesel engines. You either push up rotor radius and solidity ratio, and drop rrpm to keep cruise speed. Or sacrifice a little of the efficiency gain by generating more downwash to lift that heavy engine. A challenge yes, but not unsurmountable. Cars went from about 5% to 50% diesel sales in roughly a decade, so I would say that diesel helicopters will be mainstream in a simar timeframe.