I’d like to mention my Petrified Forest concept from a long while back in the “World Gen Variation ideas” thread.
I’m almost certain a few people already mentioned some sort of “giant forest” biome (EDIT: Hello, @Sandwitch) but I wanted to emphasize the “petrified” (or partially-petrified) status, since it’d be both an interesting twist on the concept and offer a resource-acquisition style that lets the player more realistically exist entirely within the canopy or off of the trunks and branches of the trees. Also consider needing to find creative ways to get water and food, like collection funnels/pipes and (possibly?) crude elevators or lifts using ropes.
It could also cause flammability to be a more interesting (less apocalyptic) concern: Tree #1 is still predominantly wood, so it could be set on fire, while #2 is mostly rock and less susceptible to scorching. But maybe the older (“stonier”) trees are more likely to have dangerous creatures in them, like Petrified Borers (insects) that nest inside!
Plus, we’d get some nice height variation in the world with these big forests! Just make sure the camera modes agree with such a biome and won’t give away hollowed parts of the trees before exploration!
Otherwise, I’m up for anything that brings terrain into more creative shapes, like canyons and crevices. Definitely looking forward to climate and precipitation being added!
EDIT: Also, while it’s not technically a biome (but sort of is, depending on the size), I’d really like seeing ruined cityscapes that the Hearthlings could either settle in initially or gradually reclaim over time.