Over the past 6 years this project has been cancelled and resurrected more times then I can count, though the truth is, it was never actually cancelled, many writers and directors have been removed from the project, some of which cited that the movie had been red-lighted, only to have yet another creative team working on the project a month later. The truth is, there was a definitively cancelled GoLion movie, which was going to be made for a Japanese release but was killed by WEP's (World Events Productions) ownership of the likeness of the Voltron character, so yes there was a cancelled film, but not the American version.
As for what is going on with the current film, at SDCC 2011, it was announced that the creative team had been changed, many fans of the franchise may actually find this to be a good thing, as the previous script had the Drule depicted as robots, and villains like Zarkon, Lotor, and Haggar were not even in the movie.
The new creative team of the film includes writers Thomas Dean Donnelly (Conan the Barbarian) and Joshua Oppenheimer (Sahara). The inclusion of Donnelly in particular may provide a writer who understands the sword and sorcery aspects of Voltron, rather then just turning it into a Transformers clone.
As for this creative team having a better outcome then the prior ones, only time will tell.