When not importing file extensions as part of the filename, it currently seems impossible to find other filetypes or setup smart groups listing these. Specifically, I’m trying to find all of my Omni Outliner files (with file extension/ kind: oo3). Could you please add extended searching for kind in the final 2.0 release or point me to a solution I have not considered yet.
A related note: As there are not many files with kind “Other”, I set up a smart group showing all “other” files. However, there seems to be a bug as all my imported emails (imported from Apple Mail using DTPO, extension: eml) also show up in this smart group.