Subnautica.
There should be a massive sub to dock the cyclops, with mini probes? More caves, deeper caves, more biomes such as the deep sea biome, the lava biome, the dead biome (no sea life lots of radiation) and a island biome. Land creatures could be brought to the game on islands and swimming near islands, maybe once they've added the sea emperor, it could have a fight with the Reaper. Laser gun addons to the sea moth and exosuit, stalkers could fight eachother for metal, or fight other life forms that come by. More to explore and fix in the aurora maybe to stop the smoke and fire balls. No-clip should be added as a cheat, I can't explain how much I want co-op in this game. Maybe they should add some more furniture like beds or auto slide open doors. They should make it so life forms like stalkers and bone sharks and bite your base and eventually flood it. More items like the electrical blade zaps things when you hit them, doing lots more damage and stunning the life form.