Often times when terraforming or building, one of the biggest annoyances I have is having to constantly get on/off carts.  If you don't you have that wonderful cart bug where you float ahead if you drop dirt while on a cart.  I don't think that leading a hitched cart while on foot would be out of the realm of possibility in real life, nor would it allow you to do anything you can't already do in game.  I personally think this is long overdue, would be easy to implement, and save players massive