This issue has children or is linked to all issues in Moodle tracker that have TODO or @todo in Moodle core pointing to them. Having them linked here will both prevent those issues from being closed as "Inactive" and remind developers to search for remaining TODOs when working on them.
Please note that some issues were already closed without removing the TODOs. Such issues are linked here with link type "causing regression". Separate issues must be created to finally get rid of TODOs in core.
A good starting place for this issue:
Grep the code base for
MDL-21120 - a vague issue that has been closed due to inactivity (rightly so).
Really each use should be reviewed and if not required any more the TODO removed, or more likely a specific MDL issue created and the code updated.
By my count there are 918 easily found todo's in code and only 89 with associated MDL's.