On his Facebook page, Soule responded to a fan's query about his future projects: "No, I won't be returning to Guild Wars. EverQuest has an exclusive with me for the future projects that involve MMOs. [Guild Wars] was a good experience over many years. As with all good things, it had to come to an end."
Soule was the main composer for Guild Wars and Guild Wars 2. He has also contributed to The Elder Scrolls Online main theme but will not be doing any other music for that title.
[Thanks to Bogotter for the tip!]