The existence of this special is now public, and based on the development team, I'm very confident that it is going to rock.
I contributed to a bunch of things I'm not allowed to discuss when I was consulting for Disney Imagineering last fall, and this is one of them. I've been busting to tell people about it, too, because based on what I saw, this is going to be a delight for serious Mansion nerds as well as newcomers, and Grimly is the perfect choice for it (I fell in love with his work the second I saw his illustrated edition of Pinocchio).
Disney Developing 'Haunted Mansion' Animated TV Special