With time, screens get bigger and image thumbnails get harder to see.

Thunar should allow bigger thumbnails for the purpose of efficient working with images.

Thunar needs to allow to zoom in more, so images can be viewed at bigger resolutions (I'd say up to 512x512, users with screens > 1920x1080 might want up to 768x768 or 1024x1024).

The thumbnails don't necessarily have to be generated at that size but could be scaled from thumbs of smaller sizes.