I like all sci-fi, I tend to really appreciate hard sci-fi more, but the advantage of softer versions is the release of the imagination, and in general better character treatment (not always). Thus, while soft, Ray Bradbury is one of the best ever. On the other hand, when an author can command characters, and go places usually so strange only the liberation of soft-sci usually leads there, such as Stanislaw Lem or Greg Egan, that's even better.
Lost is interesting, rather than being somewhere in the middle it's more like a mix of hard sci-fi with fantasy, relative extremes mixed rather than compromised. Lost uses the liberation to explore interesting philosophical questions from the philosophy of science, like issues of free will and determinism, so it's all good. However, my least favorite part of sci-fi on the show was the idea that they had to get the same people on 316 to return. That wasn't so bad in itself, because there were decent arguments for why the fate of the plane would be linked to the fates of the people on it, and given a "WHH but Not Always" system of time flow, that works. But when it came down to having a man's shoes, one corpse for another, etc, never explained (fiction-)scientifically was too much. It doesn't make me dislike Lost, of course, but it's the weakest part of the sci-fi so far for me.
So for me it's not great that this is all leading to another "we need these people to get off the island on a plane" focus. I think it won't affect the ending that much, and is merely bringing things to a head, but still, I wonder if they will explain why particular people are needed, or just leave it soft, "that's the way things are, some people are 'special'".
Do you think they will harden this whole area, will we hear about time tubes and the fate of people interacting in such a way to explain what it means for some people to be special? I hope so, but I don't think so, I think this is the soft side. Perhaps that's fitting, because in soft sci-fi you take amazing things on faith, and in hard sci-fi, you don't, and what is more Lost than that?