Progress I could see is like this:
- Barren, thin atmosphere worlds with no or little weather; this will allow implementation of the skybox mechanics, aerodynamics and friction heat on entry
- Barren planets with non-lethal pressure atmospheres; now we can implement persistent weather systems you can see from orbit, on the planet and approaching from the horizon, only needs simulation when someone is looking
- Barren planets with up to lethal atmospheric pressure: this includes gas giants, which will squish you if you drop too deep into them, may add new modules to increse pressure resistance, some worlds may exist where only the highlands can be landed in
- Water/liquid can be added along some of the above, first shallow systems and lakes where you don't sink, just to work in generation of flowing rivers and the like that make sense, once lethal pressures are included, deeper waters can be added with increased pressure effect, new submarine SRVs and flotation devices for your ships
- Lethality upgrades; dangerous temperatures, corrosive atmosphere, molten worlds (like water just burning), deadly weather, etc.
- Microorganisms; at this point enough worlds that can harbor microorganisms can be open and a way to exploit/research them can be implemented as a basis for more complex lifeforms
- With all environments made available, procedural generation of life on planets can be worked on
- Once life can be generated, civilization, settlements and agriculture can be generated
So by around 2027 we should have that completed. Adjust your expectations accordingly.