In what ways? I can't see it being abused any more than mounts, and other things like skills, are already. As long as the second player can manually dismount (or other restrictions, such as being a party member), I don't see how it could be used to troll with either. Also, seconding the auto-follow. I'm pretty sure Guild Wars had it and it was just another in a long list of minor QoL features that were inexplicably trashed.