According to this article in the Tucson Daily Star, proponents of a top-two initiative in Arizona are giving up, because Texas billionaires John and Laura Arnold do not agree with the strategy for passing the measure, and the Arnolds were the main source of money to pay to get the proposal on the November 2016 ballot.
The Arizona proponents felt that they were far more likely to pass top-two if the campaign for top-two was paired with another initiative, requiring organizations that spend money in campaigns to provide greater disclosure. But, according to the story, the Arnolds aren’t interested in the disclosure initiative and will not fund it.
Here is a second story, which has some additional information.