I think it would be possible for Epona to be in the game and to have a overworld that is not totally boring. If they could do that I would be alright with it. Also, I don't see how Epona has become an essential character in the game. Epona has been in 3 games.
I think... No Epona, better overworld. I do like horseback but it loses its fun after a while when you realize its the same monotonous running back and forth with nothing to do in between.