The writers have already said that the show <i>isn’t</i> taking place in someone’s mine, the afterlife or a story being told. That means that Charlie turning up for Hurley was “real” – that is, like Desmond going back in time, that the show has gone very firmly down the “supernatural is real” route.
I’ve said before on a number of occasions that s significant part of the attraction for me of complex shows like Lost is being able to work out in advance what has or will be going on. Obviously if the supernatural is real all bets are off and <i>anything</i> could happen.
I’ll still watch the show as I still want to know what it’s all about and the characters are still good but that part of my enjoyment looks to have gone for good.