That is quite dangerous, even if the lamp does strike and run up, its voltage is so low that it causes the current to increase significantly.  This leads to overheating of the ballast windings, followed by deterioration of its insulation and eventual failure of the ballast.  Some years ago Philips launched an energy-saving ceramic metal halide lamp to work on mercury 80W and 125W ballasts and they achieved that by reducing the arc voltage from 115V to 105V (lamp type CDO-H).  However even that small decrease started causing massive problems in the field of ballasts burning out, and the lamps were quickly withdrawn from sale.  With a 90V sodium arc tube it would be similarly bad (although current increase is not quite so high because the sodium arc has a very different power factor than mercury or metal halide arcs).

Another factor that I see with high pressure sodium lamps is that the rising voltage during life would allow for the ballast to run cooler.