Orius
Unrepentant DM Supremacist
Technically, since it's tied to the Mark of Warding, it can't show up outside of Eberron, unless you introduce dragonmarks into your game.
Ha! Like that's gonna stop players? Min-maxers and munchinkins never worry about such extremely mild quibbles.
Seriously, I'm sure there will be groups who will use it out of Eberron and out of context. It's always happened in D&D, there were people mixing all kinds of stuff from Greyhawk, Dragonlance and Mystara back in the 80's. Why would it stop now?