While positions in the top four may change, I feel that the teams that are there are pretty much set in stone. I don't think Pakistan and Sri Lanka are playing with enough steel to crack that top four.
As for England, I keep on expecting some sort of resistance that as yet, just has not happened. Considering the new format, it is easily the worst cricket world cup defence of all time. I'd say they are the only side out of the ten that has just not turned up at all. Even the Netherlands (who are last) definitely have a crack when they play.