I also like speculating what El Dorado will be like, however I've deduced something in the process. If Kane was waiting for you in El Dorado, that would mean either he got there without the map, or the player did. The only way to get to El Dorado is to follow the map. If he's waiting for the player, then that would mean he didn't need the map, and if he didn't need the map, he'd have no reason to hunt for the pieces. He could already have all the treasure out of El Dorado before you even got there.

Now, I dolike the rest of your theory. Maybe for more backstory, that mojo was locked up there by "Pirate Lords" or something. In order to allure people to release it, it disguised it's prison with gold. Kane wants to try to control that mojo to remove pirates from the Spiral. He wouldn't be able to control the mojo and eventually the Spiral would fall into disarray as you described it. You have to find whatever objects the original pirate lords used to lock up the mojo and use them to put the mojo back to sleep. There would be a boss spawned from the mojo to defend the item from the player.

Fearless Dolan Grant lvl65