One thing I don't hear many people talk about is new energy tech which is realized would allow for a lot more productivity, rebase the debt (GDP goes up a lot relative to debt). I wonder if that could lead to the drop you mention which may make sense as people flee the debt issue until it is rebased.
Steve Keen, Australian Economist, says GDP and Energy produced are correlated 0.99. There is always talk of new energy tech but I get the feeling it may be becoming more and more a reality. Many paradigms are shifting atm I think.