Maybe there could be a "Civ for adults". With just way less content, shorter games and a more mature art style.

Civ 1 didn't have: culture, religion, great persons, great works, armies, ranged units, luxuries, strategic resources, building placement, unit xp/promotion. Civ 1 didn't even have an improvement for forest tiles.

Civ 1 did have as extra: home city for units. Marine units had to be transported by ship - but that added an interesting mechanic, you had to protect your super important transport loaded with 7 very expensive units. Terrain improvements took a really long time so you had to have multiple settlers work on the same tile. Some superfluous things like fortresses. Small city spam ruined Civ 1.