Back to the show, I was talking to someone who had an interesting theory--Aaron is actually not one of the Oceanic 6 because he was never on the manifest of the original flight.
Who would be the 6th? Here's a thought:
Frank Lapidus.
He was supposed to be the captain of Flight 815. He just "happens" to be the captain of the new flight. AND he is not part of the large group of survivors with Ben and Locke (my guess is that he's with Sayid and/or Sun).
Of course, Kate may still be pregnant of course, and even though that might provide the 6th passenger in a roundabout way, the Lapidus theory seems more solid.