I can kind of see Fox playing Nate and Krause playing Jack.

I'd be even more interested to see what the show would have been like with Justin Theurox as David and Chris Meloni as Nate, as Alan Ball has said was his original plan.
Well The show probably wouldn't be as good. No one could have done better as David than Michael C. Hall. One of the best television performances ever IMO. And I personally love Peter Krause just as much as Nate, he always felt very raw and real in his performances.

I'd be even more interested to see what the show would have been like with Justin Theurox as David and Chris Meloni as Nate, as Alan Ball has said was his original plan.
Matthew Fox was such a similar charachter to Nate (the good guy hero always trying to do the right thing despite everything) that I can see why you'd say this. Be even cooler to see Nate on the Island interacting with Sawyer