New portal for transportation only accessible to mobs

With the latest snapshot a lot of talk has been going around about different transportation methods for villagers etc. My suggestion for this is to introduce a new portal that would be created by a new item / structure that the player would build. This portal would only be accessible to mobs so the player can't use it. (In my personal opinion it would be most fun if you had to build a structure because it feels so cheap just creating an item)

To link two portals perhaps you could perhaps name the portal with a nametag and two portals with the same name are linked. Perhaps if you were to build a structure then a specific slot in that structure could be a "linking portal slot". Perhaps you could dye the portal a certain color and with that also limiting the amount of portals that can exist. (Problem with this one would obviously be multiplayer)

When the mob walks through one end of the two linked portals it would teleport to the other portal. To make sure the mob doesn't despawn it doesn't need to load in untill the player arrives. Finally this would in general be a great way to transport mobs between bases over long distance.