I know (I use it like that of hair cards of sold 3D human models) but I want to use the main feature of hair shader, that is "conjuring" geometry. The default mode of Corona Shader is applying flat normals to splines, without the need to render them as full volumetric splines (the second mode of Corona hair shader).
With fibers being used on furniture, we're getting into billions, they shouldn't need to be small polygonal entities unless absolutely necessary. Hair geo entity with Hair shader makes that trick, but it's not possible to use it outside of box.