I would love the ability to call or whistle a nearby horse if dismounted. This could be the primary effect, and maybe the secondary is to reduce dismount chance of troops in your formation? I believe this would be in line with other perks and adds a nice mechanic that was enjoyed in Warband and many mods.
This could be implemented in the current perk tree as an alternate 125 skill perk.
I also imagine this could be a nice feature in multiplayer as a perk choice for some cavalry type units and help better distinguish them from a random infantry that happens to have stolen a horse.
@Dejan Would you mind taking a look at this and pass it to the correct people if you feel it has merit.