I have plans to do it including 3D models.
The main problem here is the limitation in memory. I experienced that if you have too much materials in a folder, with 4K textures or whatever, the memory limit will be reached and the editor will crash. In version 4 I opted for an offscreen canvas that computes the screenshots in a worker, one by one.
In my previous experiences, I also worked with designers that created too complex 3D models that blocked the main thread (editor did not respond) until the 3d model is loaded.

I understand, thanks for explaining! I added because saves me a lot of time and the editor 4 had it.

@julien-moreau what do you think about letting those previous features behind a preference flag?

@julien-moreau That works for me! If you are busy, you can also let me know what do you have in mind and I can try.

If memory is the issue, we can create thumbnails of 512x512 size. Or a more overkill approach, we could save the thumbnails in an electron-store and load them on-the-fly based on the visibility.

If the main problem is the editor hanging we could also load the thumbnails async.

Or we could have both.

Exact, what I have in mind is that we create thumbnails of 256x256 (like textures that are resized in the assets browser) and then save them to a cache. Today there is a .export-cache.json file that is created in the assets folder. We could add something like .thumbnail-cache.json where keys are relative paths to assets and values are base64 encoded 256x256 images.
What do you think?

That works! @julien-moreau I will have some free time today. I can draft something in this PR. Is that ok?

I think we can close this one

@julien-moreau with pleasure!