@jlutes - extracting from the filename is not at all possible - the original filename is lost the moment you add the book to calibre. However you could setup a regex to extract it from the filename as part of the adding books preferences - if it is something you want to toggle between for different filename formats I would suggest my Quick Preferences plugin.
As for the "tags" section, do you mean inside the metadata of the book? Again you "could" use the "Read metadata from file" option when adding the book to obtain this.
If like me you prefer not to have that option enabled (since the title/author are far too often garbage for my taste and I prefer getting from the filename), then I can see a case for wanting the Extract ISBN plugin to attempt to read it from metadata. I guess my hesitation is the complication of what "priority" any ISBN there should have. Bear in mind that every time a conversion is done on a book (or the Update metadata feature in the Modify ePub plugin is used) it is overwriting that book metadata with the contents of whatever is set in your library. There are cases where:
- an ISBN can be found in the book content and that is the preferred one
- the ISBN extracted from the book is for a different book (such as an advertisement for a related book for the publisher), but there is one set in metadata
- no ISBN can be found in the book content, but one is present in the metadata.
So I don't know which preference should be given if I were to include scanning the metadata