Several weeks ago I had the privilege of sitting down with Richard Owen Roberts to discuss revival. He was interim at my church before I cam seven years ago and I've been able to sit with him from time to time and pick his brain. If you don't know, Mr. Roberts is a bookseller in Wheaton, IL, an author/editor, and a well-known expert and preacher on the issue of revival.
Toward the end of the conversation I asked him about open-air preaching. This was well before I wrote the five main posts on open-air preaching (as well as posting several quotes on Reformissionary and Twitter on the subject). I specifically asked for his thoughts about the role of open-air preaching and a desire for revival.
He first said that he thinks most open-air preaching is bad. His words were stronger than that, but I don't want to overstate. Then he said this (this isn't a direct quote, but close)...
I can't imagine that we will ever see revival without seeing preaching in the open-air again.
I hope to return to talk to him more about the subject.