Unit Exhaustion

I believe there should atleast be an option, to include unit exhaustion in games. It may or may not affect the statistics of a unit aside from movement range. I'd say within every 3-4 turns of a unit being used without returning to a city, the movement range would decrease by -1 or so. Eventually, it would stop at range 1, so that it can still be moved into a city and regain it's "supplies". I was thinking a unit must stay in a city for a full turn before returning to maximum strength, not something that happens with stealths when you put them in a city and they return to being stealthy within the same turn. If you move a unit one turn but don't the next, it won't affect the decreasing range modifier.

I think this might make it a bit more realistic. Of course games shouldn't be realistic over balance, but this should make it so that a unit from Berlin can't travel across Asia to Beijing. It might help advertise the strategy of taking an ally's city to station troops there for re-supply, and would make Role Playing maps, UN maps, etc. take more strategy than just build a unit and chuck it across a vast amount of land or ocean. Any suggestions to tweak this or remove the idea altogether?