Originally posted by bacon:

id like a statement from the devs as to whether there will be new content trickled down into other biomes. like if they add a new mechanic, will it be present in some form in the lower biomes as well as the new one. it seems they are sticking with the linear biome design, and so it would be nice, if starting a new world, if the update brought some change. if the change doesnt start until biome #6, i think that would be a little frustrating after this long of a wait.

There's a paragraph in the Midsummer blog:

"And speaking of the Mistlands! For the teasers this week, we thought we’d share something that’s also a bit summer themed. We don’t want the Mistlands update to only be about the Mistlands – we also want there to be some new content in the earlier gameplay leading up to the new biome. A significant such addition will be an upgrade to the fish; there will be new types, they’ll come in different sizes, and you’ll be able to mount your most impressive catches on item stands! While they’re still swimming the fish will also jump above the surface, to give it all an even more atmospheric touch."
https://store.steampowered.com/news/app/892970/view/6128850732742902908

I haven't followed content discussions much on their socials, but you could also check out their Twitter accounts and / or join the Discord to ask questions.