The only reason I can see for a different landing point is disaster tolerance. For example, you could land it at Tauranga on one side of the North Island and Raglan on the other. That's close enough to Auckland to keep transit costs down (although the terrain between Tauranga and Raglan isn't particularly friendly for laying a cable) but also far enough away from Auckland that a disaster big enough to take out the landing sites in Auckland *and* the new cable would likely result in the top of the north island being a smoking crater without anyone left to care.