Bukkit

What is the enhancement in mind? How should it look and feel?

Having an option to keep horses in a world for a while after disconnecting from a server can benefit PvP servers where PvP logging to save horses is possible. Also logging out because of end of stream or going AFK for a bit and logging back in, having to resummon your horse can be inconvenient. Maybe allowing a setting in the config to automatically resummon horses within X seconds of logging out can be useful to reduce the amount of trouble.

The problem with this is that I would need to make sure the chunk the horse is in does not get unloaded, else I would then lose the entity all together.

After reloading that chunk, a duplicated horse would appear.