I've been following the development of this Liquid Piston design for a while. While I can see its utility in powering the smaller UAVs at its current design iteration, anything as large as an RV will require a huge scale up effort which isn't trivial, and swing a big propeller at low RPM will require a gearbox. Due to its natural diminutive size, perhaps they can create a gasoline-electric hybrid propulsion to solve the gearing engineering problem while maintaining the efficiency claimed by the factory. There will be a weight penalty for the gasoline-electric hybrid package but it is probably not as bad as battery powered electric airplane. Just pure conjecture.