more head movement when going at fast speeds especially on formula cars
the ability to add helmet texture and make it seem like you are inside the actual racing helmet
side head movement. right now you are able to have the head follow the mouse, but what if it did it sideways: example to counteract the g-forces, a driver will lean his head in that directions

i guess you mean adding it to the driver camera pov, the driver head does visually move to counter the gforce from the outside

There are Insim mods that do that. There is no need to implement it inside LfS