As long as Fortran is able to keep up with Python's capabilities (or any other language's for that matter), there seems to be absolutely no reason to make a change considering Fortran's history and familiarity in Physics. In other words, other languages need to make a big enough leap forward or Fortran to lag behind enough to justify a change. Your example just shows that it's fine to use other languages, and I agree, but it's not very compelling in promoting a change in language.