I'm suggesting a new Skin Builder because I (and probably many others) can't make half the characters they want because both arms/legs are EXACTLY the same, even facing the same side. I'd love it if you could customize both arms/legs to your own free will.
And teleporters are not the best idea in the world, because I can see the griefing that could ensue, but they could be 2 blocks tall, green, glowing, and an OP only feature.
I don't really care about a skin builder, but I do think the way skins are UV mapped onto the model should be changed a bit. At the least, the arms (and I think the legs are affected too) should mirror each other. As it is, you can't really make a skin with inner arm/outer arm differences, because doing it for one arm will have it reversed on the other.