I've considered the possibility a bit back that certain sequences/areas could play out of order.
The train graveyard could take place before the sewers, for instance. Unlikely, but I still expect some moments that get shifted around for pacing reasons.
Oh, for sure. I also wonder about that, although I feel that that particular "sewers-->graveyard" order is going to be respected.
BTW, it seems (according to those who played the demo) that the layout for the first reactor is almost identical to the original game, but with new transitional places connecting the "old" areas (iirc the original did skip many of those "in-between" places). I wonder if that's going to be as frequent as they can make it, although we're bound to find exceptions. Like the sewers; they look massive now so that probably doesn't apply there that much.
I'm really curious about the transitions between inhabitable places tbat are relatively safe (slum villages and the like) and hellish landscapes with weird creatures roaming free (the graveyard, the abandoned park...).