After playing the game for a short while I've thought of a couple of things that could possibly improve it. Just putting ideas out there, the game is great as is.

Sorry if something has already been suggested. I'll post replies if I come up with more.

'Big' ideas first, getting more practical as I go along.

• Rescue missions. They could involve rescuing (AI or spawned player) crew members from a sunken sub, ruins, or the open ocean.
• Missions which involve 'capture' of a creature using a net gun, which would then be dragged on board by players.
• Missions which involve salvaging material from an already-crashed submarine. Possible scenarios could be a botched explosives/chemicals delivery that needs to be completed, monsters guarding/living in the sunken sub, an artifact brought the sub down and is still wanted, a parasite zombified all of the crew into husks. Etc.
• Potentially have additional missions be made available via 'radio messages' from neighboring stations during play. If it's a mission, it could catch people off guard and be fun. Otherwise, it could be useful pieces of information, like "<Station A> to <Submarine Name>: there is a large group of <Monster Name>'s heading your way." Maybe getting these messages could be dependent on maintaining a communications array or some other machine.
• Editor prefabs: Save a selection of objects (with relative positioning and wiring information) to file. Then prefabs could be loaded and added in as necessary to remove a lot of the extra work involved in ex: placing two identically wired railguns next to each other.
• A related suggestion - editor copy-and-paste: The ability to copy and paste a selection of objects.
• Camera components: Could interface well with wifi components and work as security cameras. Could also mount them to railgun shells so that you can scout ahead of where you're going. Could also present an alternative use for railgun controllers, allowing them to function as periscopes.
• More progressive map mode: monster difficulty, mission rewards, contract difficulty, starting depth, available gear to buy etc. increase as you visit further stations.
• Blend the multiplayer sandbox/mission selection together with the single player map so that you can choose any of the three options for either single player or multiplayer. Maybe the map mode in multiplayer could be set up so that players vote for the next contract/station to visit, or the host could select it. Could potentially have players pay for what they want to bring from the store as well.
• Multiple contracts offered by stations, with the ability to choose one you like (the ability to select a contract from a list would be awesome).
• Add an electronic 'if' component, which works like signal check but will only pass on a signal if its within a specified integer range. This could help with oxygen monitors or reactor temperature displays etc without requiring knowledge of RegEx and tons of time.