I dunno.
There is a part of me that really want to support the idea of protracted battles, but I don't see any good and elegant way of implementing it.
If you give things a "fatigue" trait, what happens when one team runs out and the other has a little more fatigue?
If you go the turn limit route, doesnt that mean that you could just play fox-n-hound and tug your opponent all over the battlefield for two, three, four turns until your big army can get there? Tell me the AI will account for that...
Do the forces separate at the end of the turn, or do they go into the same square as a "battle"? If they separate, why risk losing troops in a rout if you are going next turn? string your opponent along, and then walk safely away.
Seiges are already fairly well depicted by existing TBS models, with a slow-producing city trying to win a war of attrition against several stacks of external troops.
I hate to be "that guy" but I just don't see this type of thing adding more to the game than it takes away.