It appears that K'aresh, former homeworld of the Ethereals, may well have housed a Titan worldsoul before its destruction at the hands of Dimensius:
Assuming the "Radiant Song" mentioned in this NPC dialog snippet is the same song attributed to both Azeroth and Argus at different times, as well as some form of method of the slumbering worldsoul to commune with the lifeforms inhabiting said worlds.