I've never heard of co-facilitators. At my school we just call it co-teaching. I think why you don't see it in teacher prep programs is that most teachers teach alone. Plus, how well you co-teach together is determined a lot on the relationship and the personalities of the team. It takes a long time to develop a good co-teaching practice. I've co-taught with almost twelve different teachers in my nineteen years. That's not the recipe for long term success, but until school leaders care, there's not much anyone is going to do about it.