Agreed, RotorRookie. The disadvantages of number of spark plugs to change disappear if you are running a turbodiesel radial, where the injectors last the life of the engine. The other advantage is a good spray pattern for the injectors, and a compact/light crank mech.
A loop scavenge 2-stroke radial turbodiesel is:
http://www.zoche.de/
The maximum power version is 300BHP, which would get to ~441BHP if a uniflow scavenge 2-stroke radial was developed. So on the table prepared earlier:
Zoche Aerodiesel radial: 1.8kW/kg
Concept radial turbodiesel: 2.7kW/kg
So we have a clear winner!
For automotive,where emissions are king, poppet valves have outlived sleeve valves and rotary valves because they work and don't leak oil. This is why all mass prod cars are 4-stroke, and i don't really see why similar power/weight is not achievable...
Mart