Yes, and that major barrier is COST, considering the limited units and their application.
I suspect it's more than that. I remember Porsche were developing an aeronautical version of their engines. Now they wouldn't go into that if it was simply not cost effective. They're also not short of a bob or two. They could buy VW with the change in their pocket. I suspect ridiculous barriers appear. Maybe product liability in litigation-mad America; maybe stupid FAA/JAA rules and regulations. I suppose it doesn't matter too much anymore. Boeing and Airbus can afford it and the little people can go under the radar with Rotaxes. Certainly in the UK you can't fly seriously unless you're rich and if you're rich you can afford a million or so on one of these new single-engine jets.