The books I'm referencing in this blog entry are Bruce Malina's Social-Science Commentary on the Book of Revelation and The New Jerusalem in the Revelation of John.
I must initially place my biases on the table before presenting what Malina has to write about Rev. 21:16. Having read through his social-science commentary on Revelation and most of his book about the New Jerusalem, I must admit that I am not overly impressed with Malina's method of explaining Revelation's contents. John was more than some seer beholding "visions" as a result of some altered state of consciousness (ASC): it seems that he was divinely inspired by God to behold visions and record them for later generations. I just had to get that out of the way.
While I am not a big fan of Malina's approach to the GNT, his comments on Rev. 21:16 appear to be quite helpful. In The New Jerusalem, Malina notes that the "holy city" is "of astronomical proportions, since it measures 12,000 stadia in length, width, and height" (page 54).
After observing that the city is a cube, Malina cites Pliny's Natural History which reports that a Greek stadion is equivalent to 125 Roman paces or 625 feet. The city of New Jerusalem, if measured in accordance with Pliny's comments, would extend through half of the US and "reach the height of 260 Mount Everests (the top of Mount Everest stands 29,028 feet above sea level). Furthermore, the city was of transparent gold, 'gold like pure crystal'" (Ibid).
A simple point I want to make is that the city of New Jerusalem which John saw coming down out of heaven from God must be symbolic. That is, unless we are to believe that one day a grand polis which can extend through half of the United States and is simultaneously equal in height to 260 Mount Everests will somehow literally fit on the earth as the new city further shines in all its golden splendor.
I don't think so. :-)