The , = multiple authors is not going to change because a lot of ebooks still use commas for multiple authors. So is you tend to use those types of books, you would be annoyed that calibre doesn't map commas to multiple authors
As for 3, this again depends on usage patterns. FOr instance, I usually add the first format, then download the cover using librarything. Now when fresh formats are added later, I would not want the downloaded cover to be overwritten.
The rest of them I have no problems with. In fact I believe there is already a ticket for extending autocomplete to authors and publisher.