So then, why don't we just take the path of least resistance and use whatever format is the dominant one? Oh drat, I just checked and found out that that path is to not disambiguate at all.....
I would think that the best policy is consistency... no, Australian placenames do not repeat from state to state (much). Not to the extent that it would interfere with entries... but at the same time I think that if the policy for other countries is city,state then we should stick to that.
Consistecy in itself is not that important. The most important thing is maintaining ease of editing. When people are editing an article and put brackets around something on a whim, there should be a good chance that there's a useful article at the other end of the link. The most important thing helping those odds is simplicity. _Some_ consistency helps that too--once users are generally accustomed to the fact that U.S. city articles look like "Paris, Texas", the he's likely to put "Fremont, California" in the brackets and (rightly we hope) assume that it works.
Outside the U.S., I think it's natural for people to use "Sydney, Australia" and "Lyon, France". I don't think most English speakers will have any trouble with the minor inconsistency that American cities have states and other cities have countries. Canadian ones might us provinces as well--I think Americans and Canadians both tend to think of them that way ("Toronto, Ontario"). And that way we won't have to change the title of "Montreal, Quebec" when they seceed :-)
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