I also found it very interesting. Was wondering if similar techniques could be used to estimate location (within a region, not simply 50 vs 60 hz). There does seem to be research in this area:
“The main focus of this report is to answer the question whether it is also possible to accurately determine the location of a (video or audio) recording when the ENF information is available. The first attempt to localize a recording was done in 2013 [7]. Inspired by their findings a theoretical framework is proposed to gain insight into the observation that the ENF signal is not exactly equal at all locations of an interconnected grid. Next three different localization methods are compared. Finally the new findings are discussed and recommendations for further research are given.”