The question you've got to ask is whether you want to be a guinea-pig for any product in the GA market.
I could tell you some right horror stories, from my own experience, about how warranty issues have been handled on a brand new plane, 6-figure price tag. How certain manufacturers (none mentioned in this thread) try to weasel out of responsibility, etc.
No matter how wonderful some new engine was, I wouldn't go for it unless it came with a pretty amazing warranty. I would want 10 years or 2k hours, completely comprehensive.
Plus of course a sufficiently local service organisation. In GA, very few firms trust others to pay bills (and correctly so) so getting warranty work done locally and then recovering the cost from the dealer can be a right job.
Unfortunately this is nothing to do with diesels...