That would be cool if everything is flat. But it would also need to figure out safest direction with elevation. Choose direction to minimize erosion, and control runoff. There are a ton of factors to choosing best line depending on crop/soil type.
Instead of calculating ideal lines it might be easier to have an option to visualize all lines possible within the boundary instead of just 5 (is there a setting already to show more?)
With the existing way of aiming the ab line it would also be cool to see the implement width halo on the centre line for easier squaring off outside rounds.