Open floor plans were invented as a way to cram more people into less space, thereby minimizing cost of office space per employee. They were not invented to improve productivity.
Many people work from home or camp out in a small meeting room if they want privacy. There are also over ear head phones available for free all around the campus.
At Facebook, no, it hasn't been. What parent is saying is that he hopes FB did some research on whether this will actually help or hurt productivity before risking the lifeblood of the company (engineer productivity).
Speaking of research, they should also find out how much it costs to maintain a Ghery building. If you think Facebook stock is bad now wait until you see how a Ghery building affects their bottom line.