I'm currently developing a framework, which will make use of agressive culling techniques, and I use Assimp for scene import. However, Assimp split meshes only according materials, and does not split them later as stand-alone. For example, you have a car with a set of tyres, which each share same material. But all these tyres form a single mesh (= single bounding volume), which is not what I need, I need to split them into separate meshes not only according to material, but also split into stand-alone meshes. Could You possibly consider implementing such feature? Thank You in advance.
this feature will not be implemented in Assimp because you can't give a water-tight definition of where to split. You - as a person - do know where you want to split up the mesh, but Assimp can't know that. It only can do things which work for all meshes under the sun.
But there are some things you can do from your side. For example, do not use aiProcessaiProcess_PreTransformVertices or aiProcess_OptimizeMeshes as these two attempt to find and join small meshes with the same material. You also need to watch the export options closely when exporting a scene from a 3D modelling application such as 3DSMax.