So, in Gen 7, the alola region uses ride pokemon to travel everywhere, it would be a cool idea to allow us to put saddles on certain pokemon to make them ride pokemon (AKA just a new skin with a saddle on them that we sit on to ride them.) Placing the saddle on them could be similar to the way you use held items.
Further details on what ride pokemon are and which pokemon are used as them: https://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9_Ride
This is purely cosmetic unless another use is thought of by someone else, in which case feel free to leave a comment to expand on the idea.
Thank you for reading my suggestion.