Synopis: Introduce wear-level to the machines and stuff. Make unkept machines perform worser, stop working and misbehave.
This would create games to be more active and contain lot more managing and backtracking to stuff built earlier - another level of planning (not just the machine itself, but also the upkeep cycles and its longevity-related decisions).
Would also interconnect with several other mods (ones that make broken/damaged machines misbehave, enviromental effects and damage, events etcetera).
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So this would be the hardcore-survival type game mode. Skyrim has Frostfall & Realistic Needs and Diseases for survival needs, Factorio should have Rust and Decay for for "survival needs"
Also this mod would make wonderful multiplayer co-op when people build and upkeep in combined effort; so you could have kind of freeroam emergent player roles.