Grid based lighting (Super important!): I could explain how this works but this video does a var better job than I could ever do, code included! https://www.youtube.com/watch?v=NEHMJwt7oUI It'd also make lights much more useful.
Mothership tutorial: A tutorial that takes place on the mothership to teach new players how to survive on the planet, this is actually really important because most new players get frustrated by the difficulty.
Abandoned bases and outpost's: These would be partially destroyed bases left behind by researchers and star defenders who extracted back to the mothership these could contain loot that aren't possible to make with a build tool, these bases could also be repaired by players and it'd make getting a base much easier.
Crystal redesign (Made by Valiski): https://ibb.co/0rWz16s
Earthquake frequency and intensity should increase/decrease depending on the amount of dirt on the map.
Light settings: Allowing lights to have different colours, intensities, ON/OFF ect.
Larger maps: Maps should be much bigger, so in turn much more difficult for entire servers to be griefed and the entirety of the map's dirt removed.
Crystal lamps, A glass container that once a crystal is put inside of it will begin to generate light, Intensity and size of the light depends on the crystal, the lamp is not fixed and can be dragged around just like any rigid body.
Decay: Unprotected wall's/backgrounds should rust away and eventually break, this would prevent build-up of abandoned bases preventing dirt regen and server's being greifed.
Barrel reskin: https://ibb.co/s99hWSq Yellow barrel
https://ibb.co/XpGGyqN All player buildable barrels
https://ibb.co/6NSWy1t Barrel without gradient
Tether cable: Basically a normal black cable, without transparency that has a fixed length once attached so you could attached multiple storage crates to a tank, player, ect. Could also be used to attach lamps to the previously listed objects.
Temperature meter: https://ibb.co/ygL9jzq Only shows up when the player is losing/gaining temperature if a player is getting too hot/cold the player will begin to loose health, unless the player is frozen.
Event changes and temperature propagation: Snow will bring down player temperature slightly however snow may be a sign of an oncoming blizzard the player will be warned if this is the case with a task popup warning the player of the oncoming blizzard and when it will arrive.
The meteor shower will cause the sky to turn slightly red due to the friction heating up the atmosphere and the temperature of the player will rise.
Temperature propagation will use a grid, and at the surface of the map will have the freezing/burning temperature, but for every collision with a block it will reduce the temperature until it reaches the normal temperature, some material will affect temperature more than others, such as higher level walls, if a player has low level walls then they could take refuge in caves to retain normal temperature.
Night cycle: I'm pretty sure there already was one but it doesn't appear to show up any more (at least for me). At night visibility will be reduced and temperatures will lower slightly
It'd make sense if the moon would be visible as night progresses (note that this sprite is meant look much larger than the moon on earth so SD2D's setting is not confused with earth) https://ibb.co/C88788d
Sound muffling: Works much like the temperature propagation system, pretty useless but it'd make sense to not be hearing matter amps despite being outside someone's base.
Use panels: https://ibb.co/HNjpYyy Works like PB2'S panels allows for doors to be opened/closed by pressing E on the panel. Could work with lights I dunno.
Kick/Push: When there is no other trigger-able object nearby if a player presses R it will cause them to kick or punch, it'd be very useful against Viruses, Bad dogs, Quickies you name it, so the player isn't cornered by them and instantly murdered.
Gear slots: If the player clicks on a helmet icon in the top right area it'll reveal a gear area with 3 slots for head gear, body gear, and leg gear, allowing for night vision goggles, headlamps, heat/cold resistant armour. This isn't really necessary and the headlamp could be an upgrade like invisibility.
Clone vats: Once a player has died and their rescue teleport fails to save them or they are petrified, if they have a cloning vat it will release a clone of the player but with no score and no weapons. This should be extremely costly either because of matter cost or it is only obtainable by completing enough tasks.
A quick optimization: Outside of a certain radius of an active character entities shouldn't be calculated AI, collisions, lighting, ect (This is to help servers cope with larger maps) wouldn't be surprised if this is already implemented, there should be some exceptions like matter transfer to BSU'S
Unnecessary polish:
Jetpacks should leave smoke trails behind them or even force smoke out, hover vehicles too.
Hard landings should cause a small dust cloud.
Explosions should cause smoke and screenshake the strength of the shake depending on the intensity and distance from the explosion, and flaming shrapnel should be released from the explosion.
Bullets should leave small bullet-holes on walls, and small dust clouds on impact.
Grass should lean away from hover vehicles and jetpacks.
Rockets should leave smoke trails.
Acid should sink instead of mixing with water.
Worms should flail slightly after decapitation.
At a certain height clouds should begin to spawn and increase in intensity with height.
NERFS:
Octopi (Octopusses) should have smaller range and less health to make them less of a threat.
Cubes and setyr destroyers should eventually de-spawn instead of building up.
Some of these might be worth implementing others not. Lemme know what you think?
Oh, and doors can go through walls if they're on a skybase thruster.