Well, the makers of Smash Bros have never cared much about unplayable characters.
Fighting Polygon Team, the Wire Frames, Giga Bowser, you name it - they are all clones of playable characters.
Master Hand is an exception, but he has a completely different playstyle and he's the only one who really matters to the story of Smash. The same goes for Crazy Hand.
As for Giga Bowser, the final boss of Melee, he represents Nintendo's villains by being an upgraded version of their most iconic franchise's main villain. It just makes sense. It is fairly hard to top though.
So. We have a bunch of clones and two characters who have a completely different playstyle to every other character. Something tells me that they don't really care about unplayable characters.
I've also had the idea that 0rion talked about in the last post of the first page and I'd actually say that this is the way to go. Except that I would actually prefer it if the boss randomly changed movesets during the battle. It would still be a clone, but it would make for a very interesting and intense battle. And it wouldn't even need a brand new model for itself. Just tinting the models of every playable character black and giving them red eyes would work. You know, something a la Dark Link, basically.
The hands are definitely coming back too. I've always loved how simple yet effective the "playing with toys" story is and there's no need to change it.