I'm no real Star Wars fan, but I think that the "chosen one" would be Vader/Anakin. But, instead of being the "be-all-end-all" of all the problems concerning the Light and Dark Side...he brings them back again into a standstill. Every force of nature is always in flux. Whether it be wind, or water, or whatever...what's to say, the Force, primal as it is in that Star Wars universe isn't the same way? There needs to be a catalyst for both sides, and I think Anakin/Vader just happened to be a catalytic force for both the Dark and the Light sides. Then, somewhere down the line...a long, long time from then...balance will be needed again.