It's interesting because while composers like John Williams and Hans Zimmer are obviously very popular with the general public, the western art music community is so far removed from what the general public is interested in listening to that within the canon of orchestra music compositions like this will probably never have staying power. Contemporary music is very experimental and most people don't enjoy listening to it, but that is the direction that 'classical' music has gone. Film composers may be much more popular now, but I think it will be very difficult for any of their music to have staying power for 100's of years like Mozart or Beethoven. Of any of them John Williams is the most likely to be recognized long after his death.

That being said, I personally believe that the film composition most worthy of entering the orchestra repertoire is Howard Shore's Lord of the Rings trilogy score. The intricacy and detail that went into that score is monumental and far above anything else in music IMO. The way he uses leitmotifs and develops them throughout the trilogy makes it that you can experience the entire journey just by listening to soundtrack. And the score is uniquely suited to its movie in a way most soundtracks never are. All the choir singing in the movie is even in elvish.