So a quick rejiggering of an idea you may ave already read.
For starters there is the Coordinate cards, easy to craft basicly just a simple card with a magnetic bar with coordinates incoded into it much like a credit card or hotel room key. Clearing them is easy as well as a simple use of a crafting bench can craft a coded one into a blank one. Finally they can also be dyed any color in order to keep different coded cards separate.
Then we have the Teleporter with it's new GUI, that only opens when you have a coordinate card in hand and consists of a simple input and output. Placing a blank Coor-card in the input, outputs a card with that teleporters coordinates. Then taking that card and placing it into another teleporters input will then set it to have the other as it's destination. (Card placed in A and then taken and placed into B, makes B teleport to A) The beauty of this is that you can make much more elaborate teleporter systems like a receiving pad that goes nowhere but has 10 different teleporters bring you to it. A series of teleporters that, using one after the other only brings you to new places until it finally loops you back to the beginning. Keeping a teleporter that never has a card in it and carrying around a bunch of coded Coor-Cards and whenever you need to go somewhere you just slide in the one for the place you want to go to.
As well more for SMP a couple features that would be good would be a way to lock down a teleporter so that destination is set and a way to make it so cards inserted into the teleporter are given back to you as you teleport.
Not only would this improve teleporters functionality but it could also improve the functionality of other future items.
For instance a Map table could use it to mark landmarks, personal safes and doors could use the blank cards and turn them into Access cards which can then be handed out to those that are allowed access to them, or turn that around and have access cards coded to individual people and then placed into the doors and chests to allow that person to make use of it.