Another one I was thinking of:
Duplicate in tag.
Something different than the earlier post.
When adding books to my library, I give them a default tag (Newly added).
Calibre has some functions to handle added duplicates, but this is not a complete range. If I add 10 books, I would like to say add / skip / merge for every single book based on existing books and formats.
If I add 1000 books, I want to add them all and sort it later.
In both cases Calibre can't help me. I have to add them all and look for duplicates later.
So it would be nice to have a function like:
Find duplicates one or more books containing tag...
In this way, I can skip all books I had in lib before my new collection arrived, but if one of the new books matches my library, I will see it.
(again filtering does not help in this case because I want to test all books but only want to see results based on a filter)