Simply because an international edition of TAR (any of them) has been to a location has no influence on whether the mothership goes there. TAR original has never been to Melbourne (even though it hosted the 1956 Summer Olympics) and given Bertram's penchant for wanting to get to Olympics host cities, we can't rule it out.
For that matter, if the first two legs were in fact Tahiti/Bora Bora, and the next leg is New Zealand, it is 50-50 as to whether New Zealand is one or two legs, or Australia is one or two legs. By that point, we'd be at five legs of a presumed 12, and that leaves room for countries in Africa and South America for this edition.
The last couple of seasons have been Europe heavy (I suspect so that they could do a Europe-free season) and they've done the South/Latin America back to the end city a couple of times in recent seasons, so I think that remains a possibility, especially if the end city is not on the east coast or the west coast, but somewhere in the heartland.