I don't know what is the definition of an hemisphere by the WOCT, but technically, there are four hemispheres on our world. There is the Northern and Southern hemispheres divided by the Equator and the East and West hemispheres divided by the Greenwich Meridian. Thus you could consider that Singapore is in the Northern hemisphere while South Africa is in the Southern. In other words, different cities, different continents and different hemispheres.
So, in my view, if Perth had the WOC in 2017, it would mean different continents and different cities but twice in a row in the Southern hemisphere and if Perth or China hosted the WOC. It would mean three WOC in a row in the eastern hemisphere.
But as I said, it all depends on what the WOCT definition of hemispheres is. But even if it only considers two hemispheres, West and East, the 2017 WOC would have to be held in the West, according to the rules.
My conclusion is that Montreal should be favored because it would be both in the northern and western hemispheres, which means Perth would likely be next in 2020.
Does that make any sense or is it just wishful thinking on my part?
Whatever the case, whoever wins will have to present a serious candidacy to win, and that's for sure.