FARR is more than really, really great and I agree it can be even better with upgrades like those in place.
For me I would prioritize as:
01. Launch file, Keep FARR opened and Continue searching! - "ctrl+dbl click" launches the file and keeps FARR opened but it should also keep populating results! (not all results are populated instantaneously)
02. Content Search - search for text inside .pdf, .docx, .xlsx, .pdf, .txt!
03. Ignore "accents" - add functionality to search accented and not accented files at once (search for "dinamico" and return both "dinâmico.doc" and "dinamico.txt") - it's quite unpredicted when filenames have accents or not and therefore easy to miss a search.
04. Fuzzy search - so that it may find results that are mistyped.
05. Multithread all searching - to eliminate the occasional delays people experience during searching [from Mouser]
06. Launch file and keep FARR opened but avoid safe-mode - "ctrl+dbl click" is opening apps like word and adobe pdf in safe mode - the shortcut could be changed for "shift+dbl click" or middle mouse button
07. Drag and Drop from desktop into FARR search folder - Drag and drop a file from the desktop into a FARR folder, that is shown on FARR search results, could copy/move the file into that folder (right mouse button drag and drop could open context menu - same as between normal windows folders!)
08. Drag and Drop from FARR into desktop with right click - Drag and drop a file from FARR into the desktop with right mouse button should have the same type of functionality as between windows folders (showing context menu).
09. Rename functionality - "Right click\Shell Context Menu\Rename" does not work! Add rename possibility to FARR!
10. Improved Right Click Context menu - add option to combine "ShellContext Menu" with "FARRContext Menu" - or "ShellContext" submenu could open with mouse-over (same as the "Add to Group Alias" submenu)
11. Indexing - always handy to have a faster system and be able to avoid being so picky with the amount of configured search folders!
12. Costume filetype launcher - option to override Windows settings and to use a costume application to launch files (by use of relative path)
13. Cross-platform - add macOS and Linux support!
14. Allow FARR searching while options window is open - This makes testing easier [from Nod5]
15. Ability to search settings page - "unreal commander" has this in a nice way, maybe something similar in FARR!
16. Bring FARR to front when relaunching FARR - Bring FARR to front and avoid message "Only one copy of FARR at the same time" - same as with your SSC app.
17. Toolbar shortcut items with costume icon - add option to select a specific icon instead of using the builtin .exe icon - could be handy to assign an icon to batch file as well!.
18. Double hotkey to start FARR - start FARR hitting twice a hotkey like ctrl, shift or space
01. Toolbar shortcut items with relative path are not showing the icon - "..\Winamp Lite\winamp.exe" launches winamp but it does not show the winamp.exe icon while "c:\sw\Winamp Lite\winamp.exe" does! (it does show relative path icons if FARR is restarted but it will remove them again when clicking "Configure Toolbar" and "OK")
02. Include shortcut text on context menu items - the text "Launch and stay open" should be renamed to "Launch and stay open [CTRL dbl Clk]"
Have a great day