an idea for a biome would be one filled to the brim with ice, the texture would be different to look like an ocean, this ocean with replenish its ice if you took some with a drop rate of 1-2
another idea, a plant that looks like the orange plant but its light blue and twice as rare. the affects are that if you eat it, +10 hunger, +50 oxygen. this would replace ice for the air tank recipe and make a lot more sense doing so. they would have a 1/10 chance to drop a seed if you mined them (idk why you would). this would make it easier to go farther out of your base.
last of all, iron is way too GRINDY to get in large quantities (100-200) and 50 iron just disappears late game, because everything is way too iron intensive and I have to go out again looking for iron immediately after I get back due to how much you need. the solution to this problem is either, make things use less iron in more recipes and/or make the drop rate 2-4 and larger groups where they already are.
Unpopular Opinion: multiplayer should not be added. the reason i say this is that their is not enough content in the game and some games need to be left alone.
EDIT: please add the oxygen fruit idea!