While I am very excited for the upcoming Expansion Pack, I think that Subnautica could really benefit from some small additions to the main game in order to add a little more depth to the world and gameplay. One thing I've seen in a lot of critical reviews for Subnautica is a lot of praise for creatures interacting with the environment. People love that the fauna actually interact with their surroundings and fellow creatures; biters attack other fish, stalkers scavenge metal, and different prey fish actually have different swim speeds/patterns that reflect their PDA entries. But there is less of that complexity with plant life and physical objects.
I personally strive to find every microscope and fluid analyzer I can, but they do little other than sit in my base as useless decor. The ability to repair these things would make the game instantly more immersive and interesting; they wouldn't even need to have much actual usefulness, just having new interesting details about coral or fish would add a new level of interesting to the already interesting world.
The plant life suffer a similar issue, which I find very confusing. Each individual fish has a fun PDA entry that almost always correlates to how the fish interacts with the environment, but corals and plants have a disconnect between their entries and their actual behavior. Anchor Pods and Gel Sacks both supposedly burst occasionally, predators snack on Bulb Bushes for their high water content, and Furled Papyrus may unfurl in low-light conditions; but none of these things actually appear in-game. It would be wonderful to actually see the local plantlife take on a bit of character and malleability.
I'm definitely excited for the cold arctic ice of the expansion pack, but I very much hope that the core game continues to receive love and attention going forward.