Greetings!
It's been over decade, since I wrote anything to any forum, but this game brought me back to basics. 
Some of these ideas are surely already said, in paper or in progress (or even in game already), but here are some of my thoughts.
These ideas are not meant to be "must have in-game", but more like give some extra thoughts for developers.
EDITS:
Color of the EDIT #1: RED
Overall:
- Leveling (main level, skills...)
- Economy (see Crafting section below). This would make game more MMO type and opens lots and lots of new options.
- Quests (I believe this was already in plans). If you can make even little bit same kind of system than in Conan Exiles game has this Pippi plugin, which gives many, or I could say almost infinitive possibilities to server admins to construct a wonderful server for players, I would be more than happy about it. 
- Alchemy system for potions.
- Trinket slots for character.
- Trading between characters (maybe trading window or just keep item in hand click certain button to hand over item(s) to another player).
- Talent tree for skills.
- Crafting Levels (one skill point per level. At every level player could choose either: Faster Crafting = Player picks crafting station to decrease amount of time producing items with it. For example, player likes to use less time in front of Spinning Wheel, he could spend point to decrease 5%. More Productive = One skill point gives 5% more items to from that certain crafting station. Maximum amount percent could be 50%. Maximum level per crafting station is 10 in both Faster Crafting and More Productive).
Monsters:
- I'd say, that monsters should spawn mainly in caves / dungeons / hell / specified maps.
- With "random" code, bosses could spawn in very rare cases on surface (land and water).
- Sea monsters would be nice...smaller ones inside of map and between maps bigger ones (or bosses such as seven-headed Hydra or Kraken at Deep ocean maps).
- Griffon (rare, spawn in the Mountains, Highlands)
- Minotaur (very rare, spawn in the Maze islands)
- Behemont
Animals:
- Gorillas
- Monkeys
- Giraffes
- Lizards
- Seagulls (I can hear them in-game as little bird's chirping, but can't see any) (not Steven thou 
)
- Tigers (and rare white tigers)
- Hippopotamus
- Individual fishes and fish lofts
- Bats
- Crocodiles
- Electrical eels
- Eagles
- Dodos (easter egg)
- Rooster (for breeding with chickens, in later development state)
- Sharks
- Dolphins
Character status: (optional for host to turn on or off from server side)
- Poisoned
- Fever (too hot or cold for too long)
- Blindness
- Some animals and monsters could give different debuff status.
Structures:
- World generated structures. This just gave me an idea, that players could send one of their blueprints to some kind of playful contest. Developers then could add that blueprint as a random structure in-game.
- Ruins
- Oil rigs (randomly at any ocean areas or only in Deep Ocean biomes). Some of them are fully operational and some needs fixing. Rigs could be claimable or perhaps available to all anytime. A place for bucket to collect oil.
- Underwater cities (breathable, in Deep Ocean biomes or randomly anywhere).
Food & Ingredients:
- Recipe book (character can learn to make meals)
- Meals can be eaten only sitting on chair in front of table. Meals could give character different kind of buffs for certain time (stamina, health, glowing, faster running / swimming, warmth, more attack / defence, etc.)
- Leveling for making a food.
Ores:
- Copper (for making wire, plate and coins)
- Tin (less valuable sale and making trinkets)
- Kimberlite (inside of it, sometimes can be found diamonds). Idea here is, that you can't straight find any diamonds from the game, but you have to build Modern separator to grind kimberlite first. Then you recieve kimberlite crumbs from the modern separator to Ore pan and after that you put crumbs to Washer to separate possible diamonds from kimberlite.
- Emerald (for making enchanments and valuable for sale)
- Sapphire (for making enchanments and valuable for sale)
- Silver (for making coins, pistol and valuable for sale)
- Platinum (extremely rare ore, can be smelted only via Electrical Burner)
- Zinc (for making a Bucket)
Collectable:
- Oil (from Oil Rigs, needs bucket)
- Flowers (for Alchemy)
Vehicles:
- Wagons (up to 5 players, one in front and max four in wagon. Alternative you could transfer more items, size of 4-5 chests).
- Hot air balloon (up to 3 players)
- Water airplane (one rotor small plane, which can land on water). This kind of vehicle, because at some point, the map on the server will expand quite a bit.
- Cruiser (partly roofed boat with a map and compass included) (up to 5 players)
- Viking longboat (up to 8 players)
- Submarine or Diving bell (for Deep ocean maps)
Crafting:
- Ore pan (used in rives to find minerals and with Modern separator and Washer)
- Stove for sauna. 
- Modern separator (better grinder)
- Washer (helps separate valuable ores)
- Coin mold (for copper, silver and gold coins)
- Molds for trinkets.
- Molds for alchemy
- Generator (for example, helps to pump water, gives small amount electricity)
- Electrical wire (copper ore)
- Hose
- Automated watering system on fields (needs generator and hoses)
- Scarecrow
- Bucket (made from: Iron=less durable and capacity, Zinc=more durable and capacity)
- Well (it could be constructed anywhere or it could only be built up to a certain height above ocean level)
- Electrical Burner (needs Electrical Workbench)
- Electrical Workbench (needs iron and copper plates & wire, gold and plastic)
- Plastic (needs Oil, prepared by using Refinery and Colander)
- Refinery (used for making)
Weathers:
- Maelstorm (brutal wind and lightning)
- Whirlpool (can be activated ocean areas during heavy rain)
- Lightining Storm
- Hailstorm
- Meteor Shower (Super Volcano biomes)
- Blizzard (heavy wind and almost zero visibility with extra cold temperature, only arctic biomes)
Biomes:
- Highlands
- Super volcano (lots of undeground tunnels and caves and on surface intermittent eruptions and lava flows, maybe even occasionly flying lava balls from volcano around the map)
- Craters (land area is below the sea level and waterfalls around as in Niagara Falls)
- Jungle
- Swamp
- Floating Islands (islands are in the air and different heights) (accesible only via flying vehicles)
- Deep Ocean (no islands, just deeper ocean areas than other maps)
UI:
- "Take All" -button to looting targets and storages.
- "Store All" -button to storages
WELL....There's some thoughts so far. 
I know, making a game needs time and determination.
Strength to developers.
