I think it is important to keep in mind that the approach currently favored here, in which your choice of meta-ethics guides your choice of decision theory, and in which your decision theory justifies your metaethics (in a kind of ouroborean epiphany of reflective equilibrium) - that approach is only one possible research direction.
There are other approaches that might be fruitful. In fact, it is far from clear to many people that the problem of preventing uFAI involves moral philosophy at all. (ETA: Or decision theory.)
To a small group, it sometimes appears that the only way of making progress is to maintain a narrow focus and to ruthlessly prune research subtrees as soon as they fall out of favor. But pruning in this way is gambling - it is an act of desperation by people who are made frantic by the ticking of the clock.
My preference (which may turn out to be a gamble too), is to ignore the ticking and to search the tree carefully with the help of a large, well-trained army of researchers.
Yudkowsky apparently councils ignoring the ticking as well - here:
Until you can turn your back on your rivals and the ticking clock, blank them completely out of your mind, you will not be able to see what the problem itself is asking of you. In theory, you should be able to see both at the same time. In practice, you won't.
I have argued repeatedly that the ticking is a fundamental part of the problem - and that if you ignore it, you just lose (with high probability) to those who are paying their clocks more attention. The "blank them completely ...
Barring a major collapse of human civilization (due to nuclear war, asteroid impact, etc.), many experts expect the intelligence explosion Singularity to occur within 50-200 years.
That fact means that many philosophical problems, about which philosophers have argued for millennia, are suddenly very urgent.
Those concerned with the fate of the galaxy must say to the philosophers: "Too slow! Stop screwing around with transcendental ethics and qualitative epistemologies! Start thinking with the precision of an AI researcher and solve these problems!"
If a near-future AI will determine the fate of the galaxy, we need to figure out what values we ought to give it. Should it ensure animal welfare? Is growing the human population a good thing?
But those are questions of applied ethics. More fundamental are the questions about which normative ethics to give the AI: How would the AI decide if animal welfare or large human populations were good? What rulebook should it use to answer novel moral questions that arise in the future?
But even more fundamental are the questions of meta-ethics. What do moral terms mean? Do moral facts exist? What justifies one normative rulebook over the other?
The answers to these meta-ethical questions will determine the answers to the questions of normative ethics, which, if we are successful in planning the intelligence explosion, will determine the fate of the galaxy.
Eliezer Yudkowsky has put forward one meta-ethical theory, which informs his plan for Friendly AI: Coherent Extrapolated Volition. But what if that meta-ethical theory is wrong? The galaxy is at stake.
Princeton philosopher Richard Chappell worries about how Eliezer's meta-ethical theory depends on rigid designation, which in this context may amount to something like a semantic "trick." Previously and independently, an Oxford philosopher expressed the same worry to me in private.
Eliezer's theory also employs something like the method of reflective equilibrium, about which there are many grave concerns from Eliezer's fellow naturalists, including Richard Brandt, Richard Hare, Robert Cummins, Stephen Stich, and others.
My point is not to beat up on Eliezer's meta-ethical views. I don't even know if they're wrong. Eliezer is wickedly smart. He is highly trained in the skills of overcoming biases and properly proportioning beliefs to the evidence. He thinks with the precision of an AI researcher. In my opinion, that gives him large advantages over most philosophers. When Eliezer states and defends a particular view, I take that as significant Bayesian evidence for reforming my beliefs.
Rather, my point is that we need lots of smart people working on these meta-ethical questions. We need to solve these problems, and quickly. The universe will not wait for the pace of traditional philosophy to catch up.