Planet Characterization a Good Driver for a Large Telescope

  Nobody can do it (yet) anywhere, several trying. -> Won't be solved by
  Atacama first light.

  Small distance dependence implies many transiting planets to be found.
  Each must be characterized to learn how Solar System planets figure in
  statistically. -> Lots to do for years after it's solved how to do it.

  Requires outstanding sky, the best optics, efficient drive, durable
  and reliable instruments and control systems.

  ...and even then it takes many nights per planet to do well.