A few notes (from a librarian and member of both US and British standards organizations). First, I like this idea.
ISBNs currently come in 10 and 13 character/number lengths. If incorporated, support and verification for both would be needed.
This would also allow external links into on-line library catalogues and sale catalogues.
ISBN = International Standard BOOK Number.
But, serialized publications may also come with ISSNs rather than ISBNs. ISSNs are 8 characters/numbers in length.
ISSN = International Standard SERIAL number.
For Colnect programmers, ISBN and ISSN may come with punctuation. Given the unique, required number lengths of each, punctuation is usually ignored (if displayed) in most library automation systems. But, consideration will be needed for completion of NIFs.
I would also hope that any programming also supported a barcode reader / recognition and record display. ISBN and ISSN are both commonly printed in both number and barcode formats. It's often easier and less prone to error to utilize a barcode reader.
As a stamp, philatelic product, banknote, and postal card collector, it would be wonderful if this idea where broadened to include publishing authority barcode number and, as available (as is in Russian and Ukrainian practice), print order number. There have been far too many times when I've searched endlessly for a Colnect entry when a barcode or ISBN or ISSN would have taken me to the right record in virtually no time at all. As a reminder, Colnect Titles do not use and probably never will use the publishing authority's title, whether or both in the language of the item or in an official translation. I can know from the authority's catalogue or promotional materials what they call the item, while Colnect may use something entirely different and sometimes incorrect or imprecise. Barcode/ISBN/ISSN would spare me pulling my hair out or spitting invective that, sadly, Colnect cannot hear.
This is a great idea.