There are a few problems with this that I can see.
One is that mounts are mostly useless here. With homes and tping it renders mounts largely useless, being more of a hassle than a help. As for other animals I don't really see a use or a demand. Would be a really niche market to cater to.
The second is do-ability. I'm not sure with a server panel, but with commands it would be difficult if not impossible. As far as I can recall there is no tag for if a mob is leashed, meaning it could be impossible to target leashed mobs over regular mobs. Maybe you could target leashable mobs within a certain radius but that would cause a lot of problems (Accidentally tping mobs, having to target every individual leashable mob etc.). Maybe I'm missing something that would make this much easier, but if I'm not it might just not be worth the time and effort for such a niche feature.
Not trying to rain on your parade, and I apologize if I am. Just not sure how useful or possible it would be.