Found this on Twitter, and I gotta say, it looks simply wonderful, great work!
Going back to the world map problem, I think there's a way you could give the different worlds different colors: by doing a smoothly transitioning palette fade as you trigger certain points on the map. Think of how Wario Land 3 switches the world map between day and night as an example, but instead it happening as you walk across the path to other worlds. Would that be a feasible solution?