At some point in time I realized that a campaign of X-Com: Enemy Unknown is basically a set of data manipulated by two separate games(Base building and tactical combat).
If I had infinite resources, I would apply this concept into making a layered 4X game.
City building layer- Place structures on a 3D map of a city in order to balance a few needs/desires of the citizens there in the typical Simcity style. In addition to money, other resources such as fuel, metal, cloth, and food would be produced and consumed by buildings. The efficiency of a given building would be based on its tooling and the stats of its occupants/workers. Depending on the political model, workers could be applied to specific jobs, or would gravitate towards them according to their stats. Workers can form a resource convoy capable of harvesting one resource from one nearby tile on the strategic map.
Political layer- Each city would have a set of edicts available(much like Tropico's edict system). Each edict would have some mix of pros and cons attached to it, and could either be set for a particular city, or set globally for all cities. In addition to edicts, there would be political models for government, economy, and values. Each would come with similar pros and cons. Each citizen would have faction allegiance effecting how much certain decisions impact their respect for the government. According to the government model, an election may occur every X years. Additionally, discontent breeds rebels that can overthrow an individual city to join an existing faction or create a new one.
Strategic map layer- A tile-based world map would show the locations of cities and units. Combat units transition to the tactical layer for combat. Terraformers build terrain enhancements such as roads, farms, and bunkers that effect combat, movement, and the production of
resource convoys. Resource convoy units extract one resource from any tile, regardless of adjacency. Military units fight each other by starting a battle in the tactical layer.
Tactical layer-
Using the map from the City layer, the player uses at least one unit to attack a group of at least one other unit. A point on the map is used to control it(city center in the case of a city). If the attackers control this point for a certain length of time, they take control of the tile and force all other units to retreat to other adjacent tiles, or get destroyed. If there are huge stacks on either side of a conflict, the fight takes place on a map made of the two halves of the tiles adjacent to one another with reinforcements funneled in from both sides. This allows for conflicts involving more units than can fit on the map at any one time.
Unit design layer- With components unlocked through research and development facilities, units can be created by selecting a chasis, weapon/attachment, armor, engine, and up to two special abilities. Each unit is made from parts/components acquired from factories, or trade.
Technology layer- A research building stores techs via documents. In order to build a particular building, lab workers must learn the the techs required. Lab workers learn very slowly from documents alone, but faster from other lab workers. A tech can be reverse-engineered from an existing part(faster than researching it organically), and a tech can be lost if its documents are destroyed. Death of lab workers and destruction of documents can create lost tech that can be used and repaired, but not built until all of their pre-req techs are reverse-engineered. Lab workers can be trained at one research facility and then moved to others to speed up the dissemination of information.
Space strategy layer- A 3D voxel map of space shows the locations of planets, fleets, and celestial bodies. Planets can exchange resources and units using transport vessels.
Space tactical layer- A space battle functions similarly to an on-planet battle, except that ships possess targetable hardpoints with specific functions(engines shields, comms, radars, weapons, life support, hangars, cargo bays). Collision of moving ships damage the effected hardpoints, and ships can be broken into pieces harvestable at the end of battle.