Anecdotal comments about the PA28 Thielert installation seem to confirm that the weight and moment of the gearbox and clutch assembly cause issues.
My own experience of the DA40 Tdi was that if you were two up, you needed a considerable quantity of rear ballast to stay within the cofg range. Even 4 up the DA40 cofg posistion was always quite far foward.
I'd imagine that the DR400's lighter airframe and clever wing would make the diesel perform better than a DA40, so if the loading is better then it really does sound very good.
Just a shame you have to buy a brand new one and neither the 1.7 nor the 2.0 will be available as a certified retrofit. Now where can I get £135k!