While I would love to see both beastkin and halfkin horses, I think introducing them as MLP-esque ponies is a bad idea. Having a really niche appeal and violating the trend of beastkin and halfkin races sharing their beastial traits with real-world animals, thus looking natural, aside, if this were to be added by maverik, the game's Patreon could potentially be struck down on copyright infringement grounds. However improbable that might seem.
There would be no problem with implementing this as a mod though.