I was so close to having a maple syrup KitKat. My best friend bought me one at an anime convention last month...but her sister found it. Life is so cruel.
Anyway.
Ha, knowing how the Japanese like their unusual flavours, it's entirely possible that you may see some seafood varieties in the near future.
I WOULDN'T be totally opposed to seeing a sweet potato or taro KitKat, however. Though with the sweet potato, I think I'd replace the chocolate coating with some sort of orange sweet potato-flavoured junk, like the green tea KitKat, which had no chocolate coating. I remember having taro chips way back when, and I don't really remember what they tasted like, but bubble teas come in taro flavour, so why not do taro KitKat?
Hm...OOO! Why not a sweet potato pie KitKat? You could shove some sort of marshmallow-esque goo between the wafers, and cover the thing in that orange, creamy sweet potato-flavoured stuff, and mix it with some cinnamon or...maybe not...