I for one still don't quite care for the coach.
It has phenominal rules/battalion, but I personally dont like the concept of a physical contraption in my army of poltergeists.
As for its use, yes I can see it anchoring a flank of hexes and taking out artillery/support as your mainline gets stuck in, and being a late-game monstrosity as its powered up, able to retreat + run + charge and reach incredible speed while still handing out MW's, self healing, and replenishing late-game survivors.
I wish the mourngul was more competetive and synonymous with the coach. The coach is faster, has more wounds, more overall damage output, also selfheals, also replenishes units....and costs less points