light twins?

I think there are theoetical factors against the Wankel-type rotary.

The combustion chamber shape is far from ideal and there isn't a straight
forward way to correct that. As a result, the engine leaks a lot of heat in
exhaust gasses as well as through the cooling system so there is less energy
going into producing power. All else equal (and it rarely is), the rotary
will have worse specific fuel consumption than a crank and piston.

Old pistons have one rarely discussed advantage. In the interval between
ignition and the beginning of the power stroke, piston motion is very low
and the volume of the combustion chamber is close to constant. This allows
combustion to run to completion under near ideal conditions of temperature
and pressure. That squeezes more heat calories, and therefore power, out of
the fuel-air mixture.

Bill Daniels
(I loved my RX-7)