I don’t understand how it is desirable that triangular meshes and point clouds be represented in the same data structure. There is a whole literature for point cloud specific algorithms that are not doable with a mesh, and vice versa. To start a tiny list of point cloud specific algorithms: RANSAC, RIMLS, APSS, Manifold Harmonics (exists for both meshes and point clouds, but the computation is totally different).
If a poly data can be a point cloud as well as a triangular mesh, how do we grey out unapplicable algorithms? Do we just allow them an do not produce anything when there is no vtkVertex cells?