Like everybody I've went back and forth as to whom I believe Adam & Eve will turn out to be. I initally thought it was a no brainier Rose & Bernard. I have this theory that it will end up as Sawyer and Juliet, and I feel the black and white stones represent the manner in which they die. Juliet will die as a result of her injuries. I believe it was her destiny to detonate the bomb. Sawyer devistated by this loss will choose to stay in the 70's. This will show Sawyer coming full circle since crashing on the island. His decision will be a representation of free will.
Black stone = Destiny White stone = Free will
or the stones could represent how they lived there lives
Juliet (good) = white stone Sawyer(bad/evil)= black stone