Amending trumpy81’s post:
I guess an ETA (how much time is left to finish the scan) is tricky…
- The duration of the actual scan is hard to predict as Plex is only checking the files in your library folder(s) while it’s performing the scan – however as you probably noticed that part is relatively fast.
- The duration for creating thumbnails or detecting intros can vary depending on the media. While thumbnail generation is “just some simple image processing”, the video resolution/quality will have an impact and add up as you’re scanning tons of stuff.
Personally I’m ok with the current progress indicator. But that’s not to say there’s no use case / demand for what you’re asking for. Let’s see if / how much attention this suggestion will get 
If your focus is solely on the thumbnail/preview generation… there’s already an existing feature suggestion aiming at just that. In that case you might want to comment/vote in that existing thread in order to avoid distracting votes/attention.
