It is possible that the debate regarding measuring engagement in the online world is a big waste of time because the answer is right in front of us. It's possible that Engagement is simply a strategic proxy for direct vs. indirect response.
I need to think this through some more, but the idea is that there is no true, immediate answer for the what engagement actually is. There is a direct line between strategy and engagement and that requires actionable intelligence to make it happen.
Just an idea. I need to bounce this around for a bit more. Stay tuned.