Immediately thought of this scene when reading this topic! I think that horses may add a different mode of transport for those who don't visit the major cities and petrol stations as they will become the hot spots for those with vehicles. Hopefully they add the ability to customise you vehicle to certain extent (extra fuel). Hopefully horses can have bags for storage put on them.

Really like this idea. Beans given! The idea reminded me of this scene from Book of Eli: