Listening to myself lately--sorry, it's a speech coach habit--I've noticed that I say "Okay, so..." as a way to begin instructions or bring class back into discussion. I've also noticed lots of students using the same phrase. Then, sitting in during a presentation by our school counselors, I heard it again, over and over.
For me, at least, it's recent, in the last couple months. It's all over the place. (Last year our department was inundated with "in terms of.")
Where does it come from? Who started it? When will it end?