I love the Delta Hawk and Rolls Royce alternative engine solutions, I really do, but the huge hurdle any alternative engine faces in the market is price and reliability. The huge amount of R & D as well as the certification process, combined with the STC process means that until volume sales can be achieved, the early adoptors are going to be looking at a very steep price. In many of our cases, the cost would be equal to the value of our planes. Not many of us will have that kind of money to gamble with.
It is a gamble, a huge gamble, because I don't think there has ever been a aircraft engine developed that didn't have problems. So, you and a thousand or so other brave souls pay your $70,000 to install your Delta Hawk engine and you're happily motoring along. Then it turns out that in real world flying, several of them have failures of the camshaft bearings and the FAA sends out an AD. Kind of a bummer, but you think to yourself, "Well, at least it's covered by the warranty!" Delta Hawk, a tiny start up company who still hasn't really made a profit yet, is now looking at engine swaps on a thousand planes, all on their dime. They don't have the money, so bankruptcy is the only way out. Now you're stuck with a plane you can't fly, an engine with no more factory support and in some people's cases, payments to make on a loan. I hope that all the early adopters opt to keep all the original parts to go back to gasoline.