In the spirit of Simon Terry’s “minimum viable blog post” I’ll “lower the bar” with a less than complete idea for discussion.
While I completely respect and appreciate your proposition and those of people like Bill Quirke which passionately promote the real value of internal communications, I’m left with severe doubts.
Marketing, in its “true sense” has value — yet in practice, it is generally banal.
Internal communications, in its “true sense”, has the potential revealed by yourself and Bill Quirke, but that’s rarely achieved. It’s most often just internal PR.
My personal observation is that the larger the internal communications department the more dysfunctional the organisation. I am asserting a correlation but not anything about causation. Internal communications departments to me are a symptom or perhaps legacy of a by-gone era.
You mention “even” Zappos as experiencing transition pains in its move towards holacracy however as far as I know they have no plans to ease this pain by having an HR department or an internal communications department.
I can’t help but feel this is the way of the future — the elimination of these departments.
As for the role of internal communications and “Yammer” in my direct experience with many clients that’s a default fall-back because no one knows what to do with Yammer. It’s a sign of failure, in my opinion.