Nice mock-up!
I have deleted most of the tags I got from metadata and ticked the option not to dl them.
But if I do...
So, I want the book to have tags 'science fiction', 'fantasy' and 'collection'. Metadata download blesses me with things like
'science fiction - general'
'science fiction - military'
'science fiction - American'
'science fiction - fantasy'
+10 whatever else. Most of them are such as I never want to see among my tags.
Problem is, that every time I download metadata, I get all those unnessesary tags back.
Maybe there could be (growing) database of deleted tags? So that calibre sees: yep, that tag has been rejected, no need to offer it again. Or some kind of comparison between tags in the metadata and in my library; if there are new tags, calibre could list them for my acceptance/rejection.