And just how would you like to see that implemented ?
I don't think the game could really know your intentions, because you could be saving a city just because you try to be good and use your power for the good. Or you could just make them believe you are good.(either way the problem of the town is solved)
Well it could be done if it fits the story and is based on quests, but otherwise your intentions can't be known I think. So maybe someone wants you to earn the trust of a town, and says if you do this or that for them they will trust you. And if they trust you we can move on with our plan. Or another way might be that you do something bad to a town without them knowing it, and then you make it good again and let them know about your "good deed". And as long as they don't find out, I believe that it would be bad for your karma, but (very) good for your reputation in the town.
I also think that your karma should have an influence on the world around you. If your karma is good, generally good things will happen, towns and citys will prosper. And vice versa. Offcourse this shouldn't be too much like black and white, because the npc's have karma too (also with some influence on the world). So the bigger your influence in a part of the world, the bigger the influence your karma will have. I wouldn't like to see that you do some good things and suddenly see the entire world has changed into some paradise with birds, bees and flowers. Where little elves dance with cute monkeys and drink lemonade while watching rainbows.
So the karma of the important people of a town, will partially have effect on everything that goes on there.