I'd have so much fun with this. Building a stable and all. Hopefully they will be added to exist in the main world!
Yep, as mentioned in the other posts, one problem is the transportation. But as always, our wise community, staff and developer team will figure something out.
Well, it is true (at least it was) that mobs can go through nether portals. If you go in creative mode and push some mobs through a nether portal you can get them to teleport to the nether. Perhaps horses can teleport along with the player through the portals? But once again, it will have to be fixed. Nether portals and the water portals we got are two different things.
-1 To be honest, horses sound amazing but I don't see the point. If everyone had a horse in ECC, it would lag like crazy. Not to mention horses randomly spawning in towns. I can understand in the mining world, but in the mainworld I wouldn't be too sure. Sorry.
That's a major part of horses! Can't really have them without it. If there were no breeding, then selling them at the star shop would be good. But we can't really have horses without breeding. Rather quickly, then, horses' value would inflate to less than the star price.
We can't breed any other type of animal, pigs can be ridden too and we can't breed that............why only horses then?
Because it's different for horses. Horses are spawned with different stats. Some are fast, some have more health, some jump high. Breeding horses give the offspring higher stats than the parents. It's not like breeding other animals. You should read the wiki page.
It's not going to work because some people will lag the server too much as they would only breed, until there is no space to move. Not even if they had breeding a donation, which would be kinda cool, but still not going to happen. It'll end up with the same fate of the cactus.