Apologies if this is already a wish list item, I did search for it but could not find this specific request.
I use the meta-data keywords to track threads/progressions in my story. As part of my process, I cut and paste certain sentences and paragraphs from scene to scene. Over the course of my structural editing phase, I do this a lot. It is tedious to then have to change all the corresponding meta-data.
If you could attach keywords to any amount of text (kind of like adding a comment/footnote), and if you could layer these selections, that would be great. Say, for example, you had a paragraph where the main character was thinking about another character, but for one sentence in that paragraph they were also thinking about a plot progression, then you could highlight the whole paragraph to assign the keyword of the character, and could highlight the one sentence to assign the plot progression, even though they overlap).
I know it might be complicated to display these sections, but if you like ideas, you could do it as a colored line to the left of the text beside the row(s) of text (kind of like how email chains display forwarded emails). Clicking on that line would bring up the meta-data window. You could have a check box to turn the visibility of these lines on and off.
Ultimately this functionality would just be a way to assign keywords to scenes - they would be displayed in the overall scene, not as part of a smaller component (it would be kind of like a shortcut to assign keywords). I think about it behaving like comments in a sense - where the keyword stays with the text when you cut and paste, but joins the scene’s entire collection of keywords when you go to the meta-data to look at it. I think you could still assign keywords to the entire scene through the meta-data window, and these keywords would not show up as lines to the left.