I love horses and I would love to see if you can make your horse more usefull. Instead of just one Horse for you to ride on you can also buy them as normal Barn Animals. They will produce nothing but you can offer horse riding for the children from town. The better you treat your horses the mor money you will earn. And mabe you are able to buy extra equipment to make your horses even happier. You can also combine this with my other suggestion. The horses will produce horse tail hair to make paintbrushes. See here my other suggestion about getting a dye system into the game: https://community.playstarbound.com/threads/dye-system.139830/
What he said. They could also wear different equipment that affects their speed, utility and happiness.
I've said this before, but: horse whistle to call your horse to you, wherever you are (obviously not in the mines/someone's house, but everywhere outside, basically). I know there's a mod for this, but it would be really helpful to have it in the real game for those of us that use consoles.