So the duck pond WAS supposed to be a thing?? (I’m assuming a hint that stuff was disappearing from Amy’s life?)
Oh, yes it was! To quote Steven Moffat:
“From the start, I had this single idea: that the ducks, like Amy’s
parents, had been sucked through the crack in time. And to round
everything off, in the very last shot of the series, we’d see the TARDIS
fade away, leaving us with a shot of the duckpond, and some happy
little ducks.“Then, at the last minute, we had to relocate the scene to Amy’s back
garden, and it never happened. So! There you go! Nice thought, never
happened. Oops!” [x]I actually think it still kind of works. A “duck pond” without ducks, effect without cause, something is missing, something doesn’t quite make sense but Amy doesn’t see it… it still functions as a parallel of sorts. But the actual plan would have made it a central symbol for the series arc, rather than a puzzling little remark.