Say your civ has 100 cities. Thus he should require 75 courthouses or 75% law and order
to keep the people from running amock. If he does not build the courthouses then the
cities would suffer production problems. Say they would not produce at all if there were
only 10 courthouses or 10%. And would produce at 1/4 capacity if there were 25 courthouses,
25% (Labor Riots) and so on...

I'm not sure your proposal will solve all this mess, anyway you ask for comments and I'm here ready for the job

You related plain number of cities to needs for infrastructure, still you tell too much production is the problem with large empire.

I know a long debated problem (ICS threads) is the added production of the city square, so that every one pop. city works two squares. I leave this to other clever suggestions lot of players did in the past.
OTOH, if you think great production is a problem, you must relate solution to the production itself.
Actually, if citizen growth they grow unhappiness too, and you must cope with this (with temple, wonders, military units and the like), while the raise of production affects pollution.

I think that a very large production, while resulting also in global warming and pollution on the medium/long term, must have different short term effects on population too.

Building of Factories and Mfg.plants (i.e. industrialization) should mean immigration from farms to cities, born of commuting, cultural and social effects as unemployement, raise of crime, etc.

So CivIII should relate "shields" production, Government choices (SMAC S.E.) and efficiency, forcing a player that try to raise production to full develop cities too (building courthouses, police stations/fire depts, highways/undergrounds), to balance pro and cons.

Are we on the same line?

1. Most people are unskilled citizens... Every 5 turns their Skill
Rating (SR) goes down by 1. When it reaches 50 their productivity is
quartered to 3/4 of maximum due to crime and less motivation; their parents
were factory workers so they will inevitably be as well. When the SR
reaches 25 then their productivity is halved to 1/2 and will go no lower.

2. When the unskilled citizens SR reaches 50 that is the last time you
can automatically convert to an entertainer or taxman. (75 is the last
time they can auto-convert to a scientist)
For scientists when the SR is 50 then it will take 3 turns to train
a person or his/her descendants to be a scientist. When it is 25 or
lower it will take 8 turns.
For taxmen/entertainers when the SR is 50 it will take 3 turns to train
a person to be a t/e. When it is 0 or lower it will take 8 turns.

3. Skill Ratings can be increased by building schools and libraries which
increase each citizens skill rating by one per turn. However you need teachers
to start off with and you can only acquire teachers for schools if you have
a SR of 75 to start off with. The only way to raise the SR is to make citizens
scientists (SR 100)/taxmen (SR 90)/entertainers (SR 80) and thus sacrifice
productivity.

If you keep using old, know tech your production don't drop, if not because you end natural resources (e.g. coal or silk) or the soil become exahusted (e.g. no use of fertilizer and crop rotation).

If you are forced to introduce new production methods, you may have some trouble (re-training,retooling, etc.).

I think that your fixed number of turn must be remodelled keeping in account the rate of new tech improvements: you are introducing a new advance, you must pay for prototyping (as in SMAC) but also have some price to pay for every production center (cities) you convert to the new job. As you proposed, that "price" (turn delay) can be lessened by the city developement level (universities, libraries, etc.).

As you wanted, now a large empire must take its time to mass produce a new item (supposing we can also avoid the "cheat" of rush build by excessive amount of money).

I still keep my opinion about needs of some more attention to short term effects of mass production on population (crime, immigration etc.)

Anyone else like to join with fresh opinion?

So, for the sake of a better, longer game, we are trying to add some kind of "brake" to the unstoppable production model of large but underdeveloped empire.