I think I fell in love with having indexes of movies instead of a large, single frame thumbnails (my demo video posted in the other thread only shows 2 of the 8 thumbnails) 
Even if the the assigned thumbnail was an index, it sounds like a lot more manual work. Plus I would need it for all movie files, not just mp4.
I'm really happy with my solution I've created and posted about (been using it for months). Only feature I feel that is missing, that would make this complete, is a custom column that shows if a corresponding index has been generated or not.
Having a clickable column item isn't needed anymore. right-click > View Thumbnail is working perfectly fine. Would just be nice to have a visual if an index was missing.
Thanks for posting, Leo. It might help someone.