Shakespeare's plays have survived every interpretation. Witness Romeo and Juliet. But an opera might be harder to do than a musical! In times to come, there will be attempts to do a ballet. Western themes have successfully appeared before: Rodeo, Billy the Kid, Square dance.
As to fears about bringing the outdoors, the mountains, onto a stage, a good screenwriter should not have much trouble suggesting the locales off stage. The short story of Brokeback Mountain is rich in dialogue, as well as several scenes, that were left out of the movie.
Every time the play is produced, the ambiguity of Jack's fate, for example, an end that troubles so many fans, can be presented with differing nuances. Fresh, unknown young actors will breath new life again and again into the roles of Ennis and Jack. I look forward to seeing them.