As far as I know, they have not announced anything for the theater. The guessing is that they closed the Sing-Along in advance of the opening of the new stage show opening at the Hyperion Theater in late-May. The last rumors I saw were that the Muppets were unlikely to return to the theater. Prior to the Sing-Along, the theater was often used for extended previews, so it's possible that they might use it for something like that again, but I'd like to see the Muppets return!