I am a strong proponent of the Master Teacher model, which allows institutions to scale-up their enrollments in a single online course by offering multiple course sections.
The master teacher is often a full-time faculty member (tenured or tenure-track) who developed the course.
Additional sections are taught by "co-instructors", who are supervised (and mentored) by the master teacher.
The co-instructors facilitate the discussions in their own sections, and are able to call on the specific expertise of the master teacher whenever problems arise.
Typically, the various sections have a common syllabus, common assignments, and common assessments. In addition, some online courses have a weekly synchronous session conducted by the master teacher, in which all students participate.