This is related to
MDL-17929, but different. Rather than automatically creating groups from child courses, Moodle could simply display the child courses to teachers in the metacourse. This could be similar to the drop-down list that's displayed for groups, but it would be based on child course enrollments, not groups. The drop-down list could be displayed in the gradebook, participants list, and possibly other places. In addition, the child courses could be displayed in a column beside the student's name. This would allow the child courses to be included in gradebook exports.
I agree that it's tempting to create groups, but even without groups, Moodle can easily identify the child course associated with each student in a metacourse. Some teachers will want groups and for them,
MDL-17929 is perfect, but others will see groups as an unnecessary inconvenience for what they're trying to accomplish.