The problem with that is there is a large variety of CMSes out there. It may not be cost-effective to write plugins for every CMS. Some of them may not not have

The problem with that is there is a large variety of CMSes out there. It may not be cost-effective to write plugins for every CMS. Some of them may not not have documented plugin APIs or may not have the ability to have plugins at all. Libraries may not necessarily have the budget to buy plugins or, depending on their CMS licensing agreement, might not be allowed to install 3rd party plugins. It might still be a cool little system to build though. I might try pitching it as a new (volunteer) project to my local library and see what they say.