Riven looks pretty similar to Oryx and is taken now. Is it possible that some portion of Oryx ( that isn't in a touch of malice ) is trying to bring him back? She can shape shift and the power of Oryx combined with an Ahamkara could be immense. We obviously killed Oryx in his throne world but we could of missed a shade or perhaps the piece we used in Malice has the ability to influence it's will on to others?
If that is the case... Xol (with the difference of a Throne World) will be similar