For example, when you have the GPS app or the one in the car, it will ask you where you want to go and you click where you want to go. Then it will give you instructions. It could also read out instructions to you.
This would be the first voice acting in BeamNG as far as I know. I especially doubt they could, or would use a text to speech thing.
There's bound to be hundreds of voice lines for GPS on the internet, or they could use some from real GPS. If they didnt want to, they could make like the bus routes with instructions at the top. there could also be toggle-able lines on the road,
Proper navigator would indeed be nice, for scenarios and alike it would add much to them. Huge glowing columns are not quite the way, I would think that some navigator tool would be quite bit more immersive.