I have two questions:
It seems that event DisplaceEntityEvent.Teleport.* is never fired? Will that be implemented?
The usage of (implementors of) TeleporterAgent is not implemented yet? Will it be implemented, on a short or long term?
Everything in the API will be implemented at some point.
There is a tracker for the implementation of events,
I can tell you that unless someone is working on implementing TeleporterAgent right now it is unlikely for it to be available in the first beta release (in the next few days).
There is an issue for DisplaceEntityEvent to be implemented,
https://github.com/SpongePowered/SpongeCommon/issues/271
If you would like TeleporterAgent then feel free to make an issue in SpongeCommon so that we won’t forget and perhaps make it a higher priority on the list of things to implement.