Feature Request: Error Callback Slot for Append Scene

Hi Soft8soft team,
Could the append scene puzzle have a slot for an error callback function?

Here is my reason:
We build configurators for our customers and those configurators pull from libraries of a few hundred objects. It would be impractical to load all of the objects at startup, so we load them on-demand with the append scene puzzle. Despite our best efforts to avoid it, a request for a gltf.xz file might fail. The file might not be available on the webserver or a network glitch might occur. I would prefer a method of supporting this situation gracefully.
Thank you!