Right now, I don't see the benefit of Diesel widespread. Yes, there are conversions, BUT these Centurion/Thielert/Technify have no longer TBO, they have TBR! So, no more overhaul, time's up is equal to get a new machine. Then you have the gear trouble with 300h between replacement and this itty nitty clutch, you have to have not to wreck the engine on stop. Further on, they don't run without electricity - I had so many Fadec failures, I cant count any longer.
I am keen on trying the SMA in the Cessna JT-A, as my feeling tend to see the gearless real-aviation Diesel still as an option. The automobile conversions in my eyes are not. Development cycles to press the last cent out of the buyers pocket in automotive is so short, it is not compatibel with the long cycles in aviation.
One remark to the EN590 issue - yes, there are engines out, that state compliance with EN590, BUT - BIG BUTT, this refers to the "old" EN590 only with pretty much defined max 5% RME addition - in secret they altered the EN590 to include up to 7% FAME instead of RME, which is unspecific fatty acids bio crap. This standard Diesel from tap is not compliant to aviation use.