Suppose everyone believes that we have reached The End of History, as far as monetary policy is concerned. The new inflation-targeting regime adopted by central banks has finally solved the age-old problem of the business cycle. There will be no more booms and busts. Maybe not yet solved perfectly, but the broad outlines of the solution are already in place, and all that remains is the boring technical work of bringing central banks' implementation of that policy closer and closer to perfection.
And then suddenly Something Happens. And it does not matter for this blog post what exactly that Something is. All that matters is that, whatever it is, it causes everyone to stop believing they have reached the End of Monetary Policy History. They stop believing that central banks have the correct framework to tame the business cycle. Future booms and recessions will be bigger and last longer than they had previously expected they would be.
How will the end of The End of Monetary Policy History affect investment? I think it would cause investment to fall. And that fall in investment (as a percentage of GDP) would cause the labour productivity growth rate to fall, which would cause the long run GDP growth rate to fall. And this fall in the growth rate would happen even if the growth rate of employment were unaffected by the end of The End of Monetary Policy History.