If it's ever introduced, I can't see it having anything (explicitly) to do with pixies (I could see them instructing someone on the Source via dreams, but their involvement would probably be subtext at most), since they're from a world that we're meant to believe is cut off from most people in the WoL's -- and they're locked behind an expansion, besides. After trying it in Heavensward, the devs don't seem interested in locking that kind of content behind MSQ, and it's hard not to see why.