http://www.infolatam.com/2013/01/23/chile-fracasa-de-nuevo-el-proyecto-de-reforma-del-sistema-electoral/

I think the M=2 system’s impetus to form pre-election coalitions, rather than contentions negotiations after elections, is one of the system’s strongest virtues.

It uses “sistema binominal,” so it would appear that the English “binomial” is simply a mistranslation of the Spanish for “two-member system.”

I would absolutely agree that it isn’t a system to be copied on the whole (I’m frankly surprised the GOP hasn’t proposed it for congressional elections), but I would argue that the biggest flaw in the system is extreme malapportionment, and that the system would likely perform admirably were that not the case. In particular, the “reasonable mix of representativeness, governability, and individual legislator accountability” is something that most systems do not achieve, either in being far too proportional, and therefore inefficient (Israel’s current Haredi-versus-Lapid coalition negotiations come to mind), or in the FPTP flaw most prevalent in the UK, Canada, and the USA of not representing the votes of the majority of the population in the legislative majority. Were Chile fairly apportioned, I think the system would end up reflecting a Concertación majority until the right actually won more votes.

In 2009, there was a plurality reversal. The system inherently overrepresents the second largest party/coalition, and hence manufactured majorities likely would not be common, and plurality reversals an ever-present threat. I suspect (but won’t claim to prove) that such outcomes would be even more prevalent with M=2 STV or SNTV.

(I can’t tell how much of the Chilean pattern stems from malapportionment, but the patterns described, even if attenuated, would be inherent to the system even with fair apportionment.)

Again, my point is that it is not specific enough. Either binomial or binominal makes (some) sense for describing the presence of two candidates of a given party/coalition or two legislators per district. But the essential feature of the Chilean system is as much the use of D’Hondt as it is M=2.

Though mentioning General Pinochet could very well make the Thatcherites more likely to support such a plan; they are, after all, nearly identical economic systems as well as similarly bellicose and with very strong executives supported only by a minority of the population (The Baroness Thatcher never won more than 43.9% of the vote in an election).

What do you suppose the chances are of a referendum adopting an electoral system whose opponents can, without too much overstretch, describe as an invention of Augusto Pinochet?

If a polity is going to use the principle of two single-member seats for remainder seats, though, the lowest population density rule may not be wise, as it would tend to unfairly favor conservative parties.