I just open a thread in which we can collect suggestions for future content.
interior farms for food production
I simply like that theme.
They could be implemented with complex mechanics like genetically engeneering new crop types, farming cycles in which you rotate between different crop types and designing water systems.
different ways to upgrade people
E.g. upgrading a citizien into a scientist who helps you advance on the tech tree. Different kinds of people could have different needs.
possibility to connect different buildings for different advantages (e.g. fuel building + energy production); maybe one could connect more than 2 buildings to form larger building complexes.
the game not becoming a “tower defense”-like game.
in general: more depth and complexity