Its a bit more to do actually:
It would be incomplete just to see it if a army has a path. It also changes the controls. If selected an army the 1st click (on a tile which is not the destination) will show the new rout. Second click on the tile will execute the walk order. Otherwise the army will show the path after walking the first round. This would be awkward.
And just to scare a little more. What to do if the terrain is changed. For example a new valley is created by a spell. Recalculate all routs? Only those of the AI? What if the way is blocked by an enemy or friend? Po-pup with attack order. But after walking to the enemy or before walking? I personalty do like to have the choice. Automatics will "always" do what you do not want.
Addressing all this it'll be more the two to x day feature.