sounds like a nice feature! - I'd be happy to include it in the core version if developed using standard Moodle guidelines.
Couple of links you should be familiar with:
(much of the existing old attendance code may fail this check but all "new" code added to the plugin should ideally pass)
(make sure any new functions/classes you add to the code pass that check and include correct phpdocs - ignore any failures in the existing code)
When creating new tables/modifying existing tables, please use the xmldb editor feature within Moodle to create your updated install.xml files and it can also be useful for creating the upgrade.php scripts required.
Then to share the code, please use your own account on github.com, fork the existing attendance code and make a git commit with your changes, and file a pull request for me to review.