South Dakota supporters of top-two systems will try to qualify an initiative in 2018 for their system. See this story.
The story is erroneous when it says that Louisiana has a top-two system. Louisiana had a top-two system from 1975 through 1997, but after the Louisiana version of top-two was declared to violate federal law (in the US Supreme Court decision Foster v Love), Louisiana abolished primaries and only has general elections in November (for Congress) and a run-off in December if no one gets 50%. Thanks to Mike Drucker for this news.
Louisiana has its Open Primary for the legislature and state executive offices in October of odd years. The general election (runoff) is in late November. The Congressional Open Primary is in early November of even years (until Congress changes the statute).
South Dakota elects its legislature from 35 legislative districts, one senator and two representatives from each. In 33 of the 35 districts, two representatives are elected without regard to position, so the Open Primary will be Top 4. In the other two legislative districts, the representatives are elected from subdistricts, so each will be Top 2.
The election in November is not an “Open Primary”! If someone gets over 50% they are elected, that system works fine since most people vote on election day, most don’t turn out for primaries.
In Louisiana, the Open Primary, other than for a few offices, is October of years where YEAR mod 4 equals 3 (2015, 2011, 2007, …)