Game Idea: Titan Warriors
First Gundam, then One Piece, then Zelda, why not Attack on Titan (and why not DBZ; seriously)? Titan Warriors. Imagine a big open world where you zip around on ODM gear slicing up Titans. That would be totally boss. Slicing up 200 Titans in one minute. Maybe have them wearing fur around their wastes if they want to make it kid-friendly. That wouldn't be terrible.
On that note, what if 4Kids still existed and got AoT?
I'd rather they just make a game that keeps the tone/atmosphere, I'm interested in that 3DS game if that ever gets an English release (though I'd prefer something better). I've only got Hyrule Warriors, and I love it, but that's because it fits in with the world pretty well to have the characters rampage across the battlefield with devastating magic spells cutting down most enemies with ease. I have a very hard time imagining that kind of game (where single attacks are large scale and take down tons of enemies in one swipe) working well with Titan's universe.