If the industrial zone could use a city project to make "level 1" improvements into "level 2" improvements , what if the city center is where you queue up "level 1" improvements and when you click on the city center, you can see the blueprints for the city and the build order? Instead of builders, we get different kinds of civilians for other purposes. How about the envoy is a civilian and you have to get him to the city state safely or risk sending him on his own. They can be captured and ownership is transferred. Spies, engineers for making bridges or forts outside the borders. More civilian units, but not so many as to become a grind to direct them all. They can all be captured and converted.
You still get the fun of being strategic with the build order of improvements all in one screen, but you don't have micromanage it with a builder.