Tibberius has stated in the past mounted combat will never be added to Chivalry, as much as they would like to have it in the game - they couldn’t include it on release with their budget, and it’s really something the game has to be designed for. You can see most of the maps and game mechanics would not be conductive to mounted combat at all. It would really require a complete redesign of most of the game.
Perhaps in Chivalry 2 ;)
Now that I think about it, I think you have a good point. Maybe a DLC , or chivalry 2 like you said.