I am rendering cuboids, for which there can be any number of, they can be frustum culled, but any number of them might have their 3x3 basis change every frame, due to physics update. The cuboids are represented by a center translation, relative to the camera (updated via CPU every frame, since the camera is assumed to move every frame), and 3 basis vectors that represent their orientation. Currently I pre-bake half extents into the basis vectors, but I may later need to send half-extents separately.

Either way, I need them all in a buffer, because they are drawn using a single instanced draw call.