I think we generally agree that this debris is probably from the Norwich City. I also think that human transport to the northern point is quite unlikely, and in any case it doesn't appear to be particularly useful in the context of the search for Amelia.
What is interesting and useful is if this debris was transported north by currents, wind or waves. I think this is far more likely, and very relevant to our search:
Given all we know, it is extremely unlikely that this piece of debris - as it is currently seen on the reef - could have been moved from the wreck to this spot by currents and/or wave action. The debris is steel and would sink like a stone - it is extremely unlikely that waves would have moved it half a mile North on the reef (but not impossible I admit). Additionally, the current always (?) flows toward the south.
Thus we must conclude that the debris most probably floated to the Northern point, attached to something buoyant. Then, over time, the rivets rusted out and the rest of the wreckage rotted or corroded or was swept away.
If we accept the above, there must be times when winds and waves can move a floating object north along the reef, even against the prevailing current. Notably this could occur during a storm that might also sweep a stranded Electra off the reef.
That means that a future wide-area underwater search should look not only to the South and West, but to the North of Niku as well. All else being equal, there is a 33% chance that a floating Electra was swept North.
Jon