Often there are multiple folks working on a feature and even at a requirement/user story level, there could be multiple folks working. The ability to roll the combined efforts from 'to-do' to requirement and then to the feature (and include in the capacity report) will make the traceability complete.
I second this! We have a diverse team that does a lot of "sub-story" work where if we could estimate the work in a to-do, we could potentially get a more accurate view of velocity.