Quote Originally Posted by Fynlar View Post
Yes, this is what happened for all of the one expansion we've been through so far.
It's not just expansions, it's also happened during ARR's run. Allagan Tomestones of Philosophy was the very first tomestone currency in the game with Mythology being the weekly tomestone and both currencies were eventually phased out to make room for newer currencies. There definitely is a precedent for this.