I love the backgrounds in Rasana - it seems like the ecosystems are dependent on the terrain of the continent. I bet we'll see more when new regions open up
Rasana is attached to other areas, so it can only alter slightly from what it attached to.
Look at the map. There is a huge area to fill. If each areas changes incrementally we could still have a big range of 'ecosystems' look at the the snowy mountain tops in the new bits of Aranna
And a whole of host of islands that aren't connected to anything so don't have to change just incrementally but can give us something completely different, like the spiciness of Ix