The Legend of Korra - Book 2: Spirits

 Spoiler

Somehow I doubt it's going to be Varrick, because I feel as if they need to make the next season even more grandious. Seriously,

Season 1: OH NO ALL BENDERS ARE UNDER ATTACK.

Season 2: OH NO THE WHOLE WORLD IS GOING TO EXPLODE INTO DARKNESS AHHHHH.

Yeah...I have no idea how they're going to overcome that, but downgrading to rich Varrick being the villain is quite anticlimactic. It's going to have to do with Spirits, obviously, since the merging of the worlds and all.

Also, hoping Azula and Zuko shows up. I didn't realize Part 3 of The Search was released last month and I just finished it.

 Spoiler

See I don't think it needs to be that big a deal. Maybe Varrick isn't the "main villain", but he probably will still be the crafty guy behind the scenes trying to making a gazillion dollars off of a war. Maybe he funds an international terrorist from the Earth kingdom (not Ba Sing Se, but elsewhere) and they start some pomegranate (because terrorism). Incorporate the fact that spirits can actively enter the human world, I think we could have a viable plot line where the spirits take sides in a human conflict. Now it won't be a war between humans, but a war of the humans and the spirits as they learn how to interact and discover each others capabilities.