When the selection is made, a vast number of nanobots would go to work on the person's hair, clipping, coloring (or bleaching), crimping (or straightening), and application of product, while a gentle airflow carries away the clipped ends and the spent chemicals. If you had a number of bots comparable to the number of hairs, it should only take a couple of minutes before the final result might be ready for styling into a unified hairdo. All the bots would be suctioned away, or maybe a few thousand maintenance units might be left in to keep things in order after the visit.
Or it could be the kind with the silver arms and a straight razor like this one, I don't know. It all depends on what one would willing to pay for the tech. Given the right programming, I think one could achieve results that would make today's < a href="https://web.archive.org/web/20061103102948/http://www.mariska.xdh.nl/index-eng.html">extreme hairstyles look tame.
Update: It seems to have been devised
