With quantum computing, we may not need to specify a goal for an AI.
Epistemic status: armchair ethics
[Scott Aaronson's thesis, page 3, last paragraph] talks of measuring how real something is by how much work it would take to manifest.
Therefore, we might interpret the utility of a computer in n timelines not as the average utilities of each timeline, but as the utility of the average of the timelines.
Therefore, we might give an AI the goal to gather the universe into a giant quantum computer, and let each timeline be ruled by an AI with a different goal.
If we can make sure that none of these will contain evils such as suffering humans, and at least one of them will be utopic, and we do not feel a difference between 10^40 happy lives and 10^30, this may be enough.