Thanks for the reply, kiwidude. I edit my first message because I thought the thing I was proposing was not very clear, so I cleaned it to remake the question later. But I see you understand perfectly what I meant.
About the custom columns, I regret to hear yo're not going to add it. I know it's a huge effort for the programmer to add this. And you're right, metadata download functionality can help with this, but (for example), what if you have a specific column, and you frequent a web where the free books have a download link? If you can import the site's list, and create a list on Calibre, adding also info for download links at the specific column, you then only need to click on every book, and Calibre'll open the browser and dowload the book for you.
This is only an example about the utility of this. Another: A custom column for older books (under review on a website), to get information about the version.
Maybe people thought this are very specific examples, but I work with both.
