I am almost certain they have some plans to hide it somehow. As others have mentioned, it's more important to get the show elements working first and then they can focus on hiding the backside. The easiest option will just be trees, but they'll take some time to grow in.
Honestly, it's not as bad as people make it out to be. Would it have been better were it a full mountain, certainly, but I walked all over the park back in January and never even noticed that the mountain wasn't complete. It wasn't until I came here and read all the comments that it even dawned on me.