That would be a cheap trick to introduce a new character and then have it conveniently be the guy in the coffin. I'm going to stick to my original theory that it's Ben. I don't think Sayid's flashforward changes anything. I do, however, think that we will come to see Ben's value in the world and will come to feel the distraught over his death just as Jack does in the funeral scene. Not because we feel that he is redeemed somehow or a "good guy" but because his purpose is necessary to some bigger purpose than we understand yet.