[Animats]

Wankel engines work fairly well, but the geometry is so constraining that they can't be improved much. Can't change the shape of the cylinder head. Can't change the valve timing dynamically. That's all fixed by the geometry. They got as good as they were going to get decades ago.

[maxxxxx]

Wankels are cool but they really don't have an advantage over regular engines other than vibrating less as far I know. And they have a few distinct disadvantages.

[sliverstorm]

Better power curves & higher RPM capability, so you can use a smaller, more underpowered engine for the same application.

But that never overcame their mediocre gas mileage (lack of compression/poor combustion chamber shape), oil burning (oil-lubricated apex seals), and need for frequent rebuilds.