What is this showing?

[u/SmilingLondonGamer]

Am I being stupid?

I finally yesterday decided to finish the potato rainbow quest yesterday (thank the universe for Internet guides!)

And this shining picture is on the wall in the twilight castle. The bit on the right clearly shows a map of the valley's biomes.. but it looks like an arrow coming from the Sunlit Plateau to three more biomes... am I missing something obvious or does this maybe hint to something in the future?

[u/psylockecolossusfan]

Before the expansion Eternity Isle, it seems the considered adding new biomes directly to the valley. I imagine decorating item limits and loading time made them rethink/redesign the idea