I do think lane usage might be fixable, assuming they gave modders access to ai routines.
Changing lane usage during the route might be too cpu intensive, but setting a bit of random selection during the initial path-finding should be doable.
What really bugs me with the current pathfinding is that when entering roundabouts, most (but strangely not all) car insist to enter in the rightmost lane, even if the other lanes are free and they want to take the last exit.
Had to fix a couple jams caused mainly by that.