Tom,
I found an article in WIRED that summarizes the New England Institute study specifically re: Switzerland.
CH isn't a good example to counterpose to Israel-Palestine and Northern Ireland. Ethnic conflict in those two locales carries a history of invasion in the Ulster case and an internationally-sanctioned ingathering (against the wishes of many indigines) in the other. In both instances conflict was inevitable because one ethnic group had the power. Switzerland's history is one of successful resistance to foreign incursions in which all the language groups and both religious groupings were involved.
What would have happened in Switzerland without the cantonal system? Impossible to say. Linguistically there might have been issues but religiously not necessarily. Take the Netherlands which is close to evenly-balanced between Protestant and Catholic but where all citizens speak the same language. A monument to national stability. Take neighboring Belgium, in which almost everyone is Catholic but the country is linguistically and ethnically divided between Flemish and French. And effectively cantonized as well. The nation's barely hanging together.
My real problem with the general systems and complexity theory approach to just about everything is that it tries to smooth away distinctions in the quest for common patterns. Everything becomes isomorphic. Quote from Bar-Yam: "The propensity to violence is not that different between Switzerland and Yugoslavia." Actually, yes, it is, very much so. The Ottoman invasion (remember the Field of Blackbirds) and creation of an Islamic South Slav population in Bosnia made a hell of a difference for the fate of the future Yugoslavia. So did invasions from the West which created a Catholic population using the Latin alphabet in Croatia and Slovenia in opposition to the Orthodox/Cyrillic culture of Serbia. Historical memory matters. In Switzerland it's unifying across ethnicities and in the NL it's at least benign. In many other places not so much.
Cantonization in Switzerland supposedly promotes local cantonal identity at the expense of ethnic (German, French, Italian) identity and makes Swiss-ness possible. But if you tell that to the Swiss they smile. The cantons were simply there before the country was, they say. There are other reasons Switzerland works. Thoughts of being governed from Berlin, Vienna, Paris or Rome for instance.