I like this idea, although it would be even better if some notion of "airfare expense" could be baked in as well.  The reason why Mexico is not included along with Canada and the US is (I assume, I could be wrong) because a number of attendees this past year complained that airfare to Mexico was much more expensive than airfare to the US or Europe.  Like it or not, (inexpensive) air travel seems to be arranged around global hubs; if you are flying to Mexico City from North Africa or India your best flight may take you via stops in Europe and the US.  It was suggested that (somewhat paradoxically) hosting conferences in US/Europe then allowed *more* of the global south to attend by eliminating punishing airfare to the locale.

I'm not really interested in debating this point, since it wasn't me who raised it originally in the context of Wikimania 2015 and I have no first hand experience.  But I would love to hear more about the issue from those who live outside the main air travel corridors (if only to refute the suggestion, which again I'm relaying second-hand).

It also seems like a four-year rotation might make some folks happier: US/Canada, "the rest of the world", Europe, "the rest of the world".

 --scott