Currently, some thumbnail generation parameters, like conditional sharpening, are only applied based on file type or similar information. However, these decisions do not always work well with particular files. For example, some JPG files do not need sharpening but receive it while PNGs that would benefit do not get sharpened. The default page for multi-page files is always the first page of the file, even if it is not a distinctive or useful thumbnail.
These issues would be solved by introducing per-file thumbnail configuration on the file page. StructuredDataOnCommons likely provides a good interface for this configuration system.