Pewede Cdr-files (coreldraw)
Stl-files and (3d)
Sorry, probably not. These formats are not supported by the browser, and I could not find any PHP script that can create thumbnails from these formats which are not generally supported by PHP either.
This is a bit different of course, since xslx is text-based, but it's unclear what benefit it would be to display a preview of an xslx file, which at best would be some unreadable text. Unfortunately, I can't see how this would be technically possible either, since neither the browser or PHP can read xslx ... One could perhaps import the data, render it to html, and take a screenshot, but it's clumsy at best.
I am thinking of including a generic option to manually add previews for any file types. For example if you have the file
myfile.cdr you can upload
_files.myfile.cdr.jpg and it would be used as preview. This would work nicely, but these previews would not get created automatically of course.