Since part of the existing gameplay is finding collectibles on each of the routes, I think it will be really fun and cool to have the ability to call the horse and then ride on it. It can be done in a very similar way as in Witcher 3, especially since it is using the same engine. Just whenever on foot, click the button to call the horse and it will appear from somewhere. When you don't need it simply climb down and will walk somewhere and will disappear. Also, it will be something that will make train sim world gameplay completely different from other train sims.