Sewer & Mag-Lev Track Expansion
Mole people!

I would love to see sewers and mag-lev tracks finished/connected across all sectors. I think there's some obvious hazards that should be involved in navigating these things both to protect newbies and challenge those who would use them but I think underground city infrastructure that ties into grid/sic/power/lighting/traffic with the right skills would be awesome as a reward to those brave explorers.