DH - YES, zones of control for purposes of SUPPLY would be adding a whole new layer of complexity for THE COMPUTER PROGRAMMER. If you are cut off - SURROUNDED - you are out of supply and your strength and movement is cut in half (if you can move more than 1 as it pertains to movement). Pretty simple for the player, huh?
I agree with you Winston that cities surrounded and under seige for prolonged periods of time would collapse with regard to their INDUSTRY and their ability to provide an increase to the defense of its garrison, but there would have to be variants. The larger the city, the longer it survives. Also, take into consideration the scenario of Leningrad during WW2. There was air supply and sea supply, and although both very limited, the citizens managed to hold out for over a year.
STACKING. There has to be a cut-off point. Where I don't know, but there must be one SOMEWHERE. The STACK of DOOM concept, unchecked by reason, is - well, pedestrian.
TIME - Technology development controls the rate of time - Players acitivites modulate it.
Exception - the rare but few trumping exceptions to the rulership of Tech-time. 100-50-10-5 and 1 year turns unless there is war. Peace time movement/activity and production are always gauged at 1 year turn intervals wherever they are in history. The however rare, yet plausible situation, entailing no ground movement/activity combined with no production causes a switch to 5 year intervals. After 5 turns at 5 year intervals, the AI switches to 10 year intervals. After 5 x 10 year intervals, the AI switches to 50 years and so on maxed at 100.
Warfare - When a war starts great wonders unrelated to war cant be produced by the warring countries, turns are switched to 3 months for all players and the production time for anything UNRELATED to warfare, minus a few possible exceptions, is multiplied by 4, and remains so until peace is resumed.
Given the above, time would almost ALWAYS be moving very VERY slow initially until the the settlement activity is out of the way. Much of Tech would be out of sight, so that is where standardized city production and time management comes in. It would require a whole new interface for the player, but would work very simply. The time stream would always be reaching for the upper limit of 100 years whenever possible. But, the fundamental control to time is the development of technology. Technology is merged into the primary interface for management of ones nation, know as a master control screen - and is where the player spends most of his or her time - instead of gazing at a map - unless the player chooses to. On the main control screen is a minimap of all of land and inventory of the player cities. The player sets up all city production from there, unless he chooses to switch to micromanaged production through each individual city (as it is now). The player instructs his nation to build x amount of troops, tells it to place them ih whatever city or cities countryside/or border frontier - tells his cities to build whatever developments across the board - All within a Time Block gauged by Technology. Im Iron-age for example. I can only build certain things and all of those things will be built across the board wherever I generally or specifically want them built during the time it takes me to reach the next level of Technology.
At least thats how I would generally handle what I consider to be the second biggest problem with CIV next to its combat system - its **** up time system.