Image for clarity.
As shown you could only move to layer 2 by walking on the special tile then moving northwards. After the player would move on to the 2nd layer you would basically be just like existing on a different mining level except you would still be visible by the players on layer 1.
It would make the world very interesting as you could have houses, towers or other buildings exist on the same area and never be instanced as its now.
Maybe its still difficult but yet an interesting mechanic if implemented.
Edit: Just a small refinement to clarify a small problem that would show up with using a single vector tile.
If haven 2 walking mechanics are based on the similar haven 1 walking mechanics it would make more sense to have 2 vector tiles adjacent to each other. By haven walking logic you teleport small distances from spot to spot. In this instance if you mini hoppe from one vector tile to the next you basically change layer. But if you walk off the vector tile you basically walk of the layer that the vector tile belongs too.
In simple terms. Walking from 1 layer to another would mean you would need to walk on to the south vector tile. Then walk on the north vector tile, as you walk on to the northern vector tile you change layer and then can simply walk off it and exist on layer 2. But walking on or off a vector tile wouldn't change your layer, only by crossing one vector tile to another would your layer change.
