[compurandom]

I don't think there's a way to append to a column from a metadata plugin unless the column is already a tags column, in which case it always appends. (Languages is a tags field, so that works.)

I'm also not sure how to do a custom column, but worst case, we can try to get a feature added to calibre.

It already gets publication date.
I notice this book has both a publication date and an inception date. I was considering using inception date when publication date was not available.

Publisher is a field that typically has multiple values even for a single edition. How should that be handled?

"All available identifiers" is a tall order. Wikidata has a *lot* of them.
"All identifiers used by this list of books" is more tractable. Also, some identifiers have messy properties or may otherwise not be appropriate; for instance, with this book, the NNL work ID has 12 instances; do you really want all those added to calibre? If I add identifiers, I'd prefer to add them one at a time and give users options as to which ones they want imported, but this could quickly become a long list. This might be something appropriate for a "tweaks" style calibre preference.

Some of these fields are edition specific, and this plugin is currently specifically designed to not match to a specific volume; in fact, for the first publication date, I was considering traversing the "edition of" links to find the first edition printed. How would you propose selecting the correct edition for edition specific fields?