Support for triaxial ellipsoid projections

Hello, I was wondering if there are plans to implement support for triaxial ellipsoids. Although I see that the semiMedian_Axis is something that is included in the documentation for ellipsoids, from my understanding it is not something that is used anywhere. I want to be able to eventually plot projections with Cartopy using custom triaxial ellipsoids, which I know requires PROJ support. Thanks!