That would work for some of them to import them in but a huge number of the physical library are pre-ISBN.
I do see what you mean though about using a barcode scanner to populate a text document with ISBN codes and then importing those into calibre.
For me the goal is to have someone else do the programming and me just use the software.
I don't have a particular bent or passion towards programming. I have passion for reading and collecting books.
So for me its all about finding and using solutions others have made to meet my ends.
that's one of the reasons I always donate towards the opensource projects of the software I use such as calibre, or egroupware and any of another 7 or 8 software packages I use a lot from open source developers. Much rather support those people and that model over most closed source developers. The products tend to be better, more bug free, and have better support from users online.