I ran into this article some time ago, and am not sure whether or not this is ISIS's real aim or not.
Truth be told, even though one is seen as a terrorist organization and the other as a legitimate regime, there are far too many similarities between the two, at from the perspective of being on the outside looking in.
Still, it is an interesting topic, and quite relevant at the moment, so it seemed worth sharing here:
Middle East Time Bomb: The Real Aim of ISIS Is to Replace the Saud Family as the New Emirs of Arabia by Alastair Crooke, Fmr. MI-6 agent; Author, 'Resistance: The Essence of Islamic Revolution' Posted: 09/02/2014: