The Rand Cam and Dyna-Cam engines certainly are a lot smoother in their torque delivery than a conventional piston/crankshaft recip. One or the other could easily find its way into that 250 - 400 SHP market as an economical alternative to a small turbine.
BTW, a 2-stroke diesel does not suffer from the same efficiency problems as its premix/petrol brethren. Their power/weight ratio goes up a lot, while their fuel-for-hp rate gets only a little worse. If you need the power, 2-stroke diesel is the way to go!