I don't think that Cessna would risk a whole new plane on a Thielert diesel.
I also think that Thielert wouldn't risk their commercial future by marketing a diesel engine in the USA, before it has been thoroughly tested by European guinea-pigs.
The IO-580 is interesting. I had a reason to look at it a couple of years ago, and found that Lyco introduced it c. 1995, so it is 10 years old! I suppose, so few new planes (of the right size) are coming on the market these days that there were no takers. The VUT Cobra uses it, interestingly.
The new Cessna looks nice.