(Anime Version) Hao wasn't actually defeated.Obligatory: When the Spirit of Fire absorbed the Spirit King, Zeke had the power of what is essentially God. He could have simply made it seem like he was defeated in order to avoid anymore trouble from the rest of the world. He now governs the world in secret. He speaks to the Patch tribe, as the King of Spirits, and has them host the Shaman tournament as usual. When, in reality, the winner of the tournament will be allowed into Zeke's council rather than claiming the crown. In this way, he will begin to create his Shaman only world.
(Anime Version) Hao won't be back for a sequel.His status as a cold-hearted villain is played pretty straight in the anime. Of course being cruel and uncaring, even to the 'Great Spirit' itself sure didn't help his case much.
All the things that people attribute to aliens (Stonehenge, the Pyramids, etc.) were built by Shamans.The anime and manga certainly seem indicate as much don't they?
Time Lords are Shamans!They're the result of a Shaman King that made a Shaman-only planet in the very distant past.
There will be a truer to the manga Shaman King anime.Something like Fullmetal alchemist:Brotherhood,created because of the popularity boom and as a prequel to flowers.
Hao is going to find being the Shaman King sucks.After everything he did, people ARE NOT going to just believe him when he says "I did a lot of terrible things, but now I'm good." He'll have to work himself to the bone to get people to start trusting him, and he probably still won't remembered too fondly after everything he did.