Steel pipes & pumps with greater throughput and longer underground distance.
Mods introducing new content into the game.
Augmented or new ways of transporting materials - belts, inserters, pipes!
Things related to oil and other fluids.
Is there a reason you put the upgrades.lua in the "attic"? Would be handy to be able to use the upgrade planner. I can create a PR for you if you are busy.
