Wankel has great power density.
But deficient in efficiency (fuel econ) and emissions.
Those are what has kept it out of mass production cars.
In its fuel economy limitations and its high power density, the Wankel resembles a gas turbine. I was interested to learn recently about the Whittle gas turbine development. The Germans put the resources behind their jet aircraft program that the British mostly starved Whittle of. What was interesting, though, was that although the German axial flow design was very successful in the Me-262, and centrifugal jet engines have been unheard-of for many decades, Whittle fixed on the centrifugal principle early, and for a substantial reason - the need to withstand a high turbine inlet temperature, or TIT.Low TIT means low efficiency and low power, just as low compression ratio is an efficiency killer in a reciprocating engine. It makes sense that a centrifugal design would be better able to resist high TIT because the outside of the centrifugal turbine - at the turbine inlet - the stress on the turbine would be a minimum. The inner area of the turbine, exposed to lower temperature because the gas has expanded considerably in the outer part of the turbine, is where the material must withstand the centrifugal force exerted on the outer as well as the inner part of the whole disk.
In that sense Whittle had it right - the report I heard asserted that there is still extant a flyable British jet with a Whittle centrifugal engine built during WWII. Whereas the Germans, constrained as they were by materials availability, couldnt build their axial flow turbines to fly for more than 30 hours before overhaul.