Just My suggestions

[MrQuaid]

Zones, since you can go pretty far away from your starting area would be cool if you could set up zones (Areas where duplicants must stay in). Example would be setting up a mining camp etc. For this to work would need some extra things, hence the next idea.

Storage container shoots, a shoot that you link to other storage units that acts as a resource transfer like pipes transfer fluid. The shoots would be on the same layer as the vents so planning would be needed.

Mini Teleporters to transfer duplicants to other zones, would be cool, later research stuff. 

Background textures when building rooms, like starbound, just for cosmetics. 

Tools, like miners drill, builders tools, cooks tool etc, something that would add a bonus, maybe require small batteries to run. 

Junction boxes, a place to run a number of 120 wires where the duplicant can operate the on/off 

Advanced mushbar creater with pip intake so no need to bring water

More recreational things for the duplicants, like games, books, etc to do.

Different exosuits, maybe ones for specific things like heavy ones to carry more stuff, ones that protect against heat, others for under liquid.

Just some ideas, love the game.