Due to differences in Kind labeling, the same (PDF) or similar (PowerPoint and Keynote) filetypes are not grouped together when sorting by Kind alphabetically.

I’d like the Kind column in the Finder to provide secondary sort options, similar to the Album column in iTunes 7.

Clicking on the column header label would switch between the alphabetical Kind sort and Kind by Category, which would group files by the basic type. The mockup shows PDF, other vector formats, word processing, presentations, spreadsheets, and finally bitmap images. The order of categories would need more consideration.
Issues
- The category is not explicitly stated.
- Most people don’t know the difference between a vector-based image and a bitmap, making the groupings seem arbitrary.
- There are many custom filetypes that don’t fit easily into a category; what is a Curio document? Technically, it is a package, but it’s essentially a compound document.