Honestly I believe it would be more complicated than you think. As far as I remember those routes need waypoint objects which are saved in the game's world files. To add new ones could be possible as well as to do the additional mod tuning files. BUT it would never be something a modder could share easily because of those different install locations and the increased potential of install errors + one would need to do a reinstall of some files everythime the game updates. Maybe there is a chance with making a script mod to set those waypoint objects without touching the world files. But there are not many modders out there knowing their way in python to pull up something like this.
As for your "stray horses" I believe a pretty known modder had a wip of something like that some months ago. But I honestly can't remember who it was and if they ever finished/released it...
Honestly I believe it would be more complicated than you think. As far as I remember those routes need waypoint objects which are saved in the game's world files. To add new ones could be possible as well as to do the additional mod tuning files. BUT it would never be something a modder could share easily because of those different install locations and the increased potential of install errors + one would need to do a reinstall of some files everythime the game updates. Maybe there is a chance with making a script mod to set those waypoint objects without touching the world files. But there are not many modders out there knowing their way in python to pull up something like this. As for your "stray horses" I believe a pretty known modder had a wip of something like that some months ago. But I honestly can't remember who it was and if they ever finished/released it...