Brian has created a double-high, 8-board version of the plyrack, with two backboards rather than the single one found in the original.
For greater stability, he attached the backboards using metal brackets, rather than hinges. He also used four front cross members (also attached with brackets), in place of a single, slotted front cross member.
Brian has added pipe insulation around the arms to protect the bottoms of the boards from dings. I haven't found this necessary, myself, but it might keep your boards looking nice in the long run.
With a rack this tall, you'll probably want to secure it to the wall or ceiling at the top, especially in earthquake country. Bungees to hold the boards in place in the event of a tremor might be a good idea, too.