I was messing around with portable teleporters. I noticed I could teleport from anywhere I was, in any situation (as long as the device is charged), to another place at a heartbeat.

What if there were a 5 second delay between when you press "Teleport" and the event, and perhaps with a cool animation?

This is a sort of a "balancing" issue: while the normal teleporters require you build 2 of them and you go/walk to them to teleport, the portable teleporters are always at hand, they can work immediately, and you can get away with almost anything, such as a hostile mob siege, falling in lava, multiplayer combat etc.

Added a config option, "PortableTeleporterDelay", that defines the time in ticks it takes to teleport after pressing the teleport button.

100% agree on that! And also that it takes more energy, so the portable teleporter becomes more of a couple-use emergency thing rather than a quite OP gadget.

Definitely a good idea. I might add that it makes sense for the portable teleporter to take more energy than the one that has a frame to form the field in- it has to use more energy to define the area of effect/push the area of effect outside of itself.

Yes.

i would suggest the inreased power usage.. but also a "advanced" teleporter remote that offers a quicker teleport or a "shield" while teleporting?

This makes more sense for single player, but SMP servers are usually laden with instant alternatives such as /home /spawn or /back.

but SMP servers are usually laden with instant alternatives such as /home /spawn or /back.

Yes, but this is a decision of the server staff on their own server: some may want Civ and PvE: staff can give players ores or valuable drops, which would render the digital miner useless; others may want PvP: usually PvP logging is strongly discouraged, so would be instant teleportation.