Hi!
Would .glTF/.GLB suffice instead of .fbx? It supports hierarchical scenes, pbr materials and has good support with most 3D modeling software (sometimes via add-ins). I am asking because other ppl asked for .fbx too (see this thread) and it seemed that they could make use of glTF as well.
(Note that Shapr3D currently doesn’t have glTF export either, nor planned to support it at the moment. But if we put a new 3D mesh format export on our roadmap, it would likely be .glTF instead of .fbx.)