- Vassal civilisations as a result of a national wonder (Canada for French, Russians for Ukrainians, Australians for English, Brazil for Portuguese, Byzantines for Romans, etc). The idea is to use it when you see you overgrow and your economy is crippled.
- Crusades/Jihad units. 1 such unit allowed per civ at any time. 10 strenght, 1 movement, + 100% vs melee, +50% vs mounted, +30% city attack, can enter rival territories without triggering war, can only attack an holy city, or a city with your state religion belonging the the nation controlling your holy city. If this unit is destroyed, - 2 moral for 50 turns, rebuilding it get a +100% construction bonus in it home town. If this unit conquer the holy city, + 1 morale as long as it occupy the holy city.
- Holy grail unit, this unit is created after a national wonder is built...it makes any city Holy, granting it the same bonus as the holy city or a weaker version. Using it inside your empire is interesting, but sending a crusade on it if you use it on an enemy city might also be quite appealing.
- Defensive units tree. Units which will not invade enemy territory nor leave your cultural borders, only defend your country and attack only place where you have a cultural dominance (they still can't enter enemy territory, so your cultural dominance must get them a path to the city you want to attack).
- Plague, but not like in Rhye and Fall of civilisation. It would needs to be fined tuned to cripple peoples with heavy armies and never remove the last defender...ghost towns are not logical...there should be no more then 3 in a game, and 1 should be predictable (either happen when a tech is discovered, or at a precise moment, or when all civs make contact with all civs).
- A use for extra ressources beside the corporation thingy. I think extra ressources should AUTOMATICCALLY build some extra units inside the capital (easy on design, work and all)...an extra wheat alone might produce 1 extra worker every 100 turns or whatever...extra metal might be 1 extra melee unit every 100 turns...and then an extra ressource of the same time reduce this slightly, not much...like every 92 turns or whatever...each ressource should do something different if possible, even if this isn't always units...stone for example might give you a free building, not giving you the choice, automatically, in a list pre-determined, if the capital already has all these building, maybe it can give it ahead of the tech tree finding...or then give it to a neighboring city that needs 1 of the building in the list.
- Mostly Peace option. Now there is a always peace and always war option...a Mostly Peace option would be neat, where war between civs is not impossible, but extremely unlikely, so it may happen only a few times in the game, and it is prolly going to be in the late game. The player might be limited to 2 wars declaration in the whole game, and add a limit of only 1 per era.
- Space ERA. Once a civilisation complete the space ship, the game should enter the SPACE era. Earth is a neutral zone policed by Canada (or whatever UN-oriented country that isn't going to be in the space race). Earth is the only planet colonized by more then 1 civilisation and war here is completely, and totally, impossible, Canada (or whatever country) would beat any aggressor bad and produce warships endlessly, yet never exit Earth area so it get really messy around here (make it funny to see hundred of units around here). Every civilisation deamed worthy of space competition can access Earth production, but they each see a different All civs (humans mostly) share this area freely, it has to look like a big mess. The country which win the space race is the only one with a colonisation ship at start. The cultural developpment of Earth should represent the % of what the game was upon entering this era and be relatively if not totally static, for the civs % of Earth population. Every civ bonus should be changed for this new ERA and there should be aliens races, some of which don't understand there are different humans civilisations, some of which understanding it fully...Earth could be conquered by aliens, if this happen, it is game over...maybe make this unlikely to happen, especially with Canada been crazily policing around!
Yeah, units which share the same stack in Earth area could attack each other just outside the area. Aliens races should not have a similar developpment to Humans, some of which should have an outrageous headstart...other could be backward, nonetheless, they may have very weird or different goals...make it funny.