I have not read the 2012 70E yet. But my understanding is that all of the information we have on arc flash came from experiments in which someone blew up a bunch of equipment, measured a bunch of stuff, and came up with equations that described what they observed. In other words, the equations used to calculate the arc flash energy are all empirical. So if nobody has yet blown up a single phase panel, then there are going to be no equations that describe the arc flash hazards of a single phase panel. If you want to call that a ?technology gap,? then go ahead.
Last I heard, there were no equations for DC systems, single phase systems, systems rated lower than 208 volts, and systems rated higher than 15,000 volts. Perhaps some additional experiments have been done recently, and additional systems are now covered by arc flash equations.