This is unrelated to EUOL's universe, but in the Wheel of Time, the one power was used to travel to other worlds. Regardless, there doesn't have to be a prior instance of magical world travel in order for Brandon to come up with something. Technically, if an Elantrian knew the exact distance, he could probably travel there, although I imagine it would be a one way trip, as the Dor would most likely be non-existent in the other world. I'm sure perfectly good ways to get around that problem could be thought up, as well. The coolest thing would be that the shards powers are the same in all the worlds, and it is the genetic makeup of the people that determine how the power is manifested. that would mean that Mistborn are Mistborn everywhere, along with Elantrians, Awakeners, etc. It would make for fantastic battles between worlds. Then imagine if the different races bred? What would an Elantrian Mistborn be able to do? This is why Fantasy rules.