The premiere is scheduled for June 2013 in Madrid's Teatro Real.
There is an interview between Juan Antonio Muñoz H. of El Mercurio and composer Charles Wuorinen about a new project he is working on, "Brokeback Mountain" - the opera. Annie Proulx, who wrote the original story, wrote the libretto, so the opera will not necessarily compare to the film. Some of the changes are women playing a slightly larger role, there will be no physical expression of sex on stage, but rather the emotions will be sung, and, as there are no close-ups, there are more internal dialogs.
The above link is only a translation of the original article/interview, but it illuminates some interesting aspects about writing an opera, working with the subject matter of homosexuality and how Charles Wourinen is approaching this work.