Hubble volume
It matters. There's a good chance our universe is infinite, but there's also a good chance it's physically impossible to escape the (shrinking, effectively) hubble volume, superintelligence or not.
I'm inclined to think that if there was intelligence in there we'd probably see it, though. UFAI is a highly probable way for our civilization to end, but it won't stop the offspring from spreading. Yes, it's really big, but I expect UFAI to spread at ~lightspeed.
X-risks
UFAI's the big one, but there are a couple others. Biotech-powered script kiddies, nanotech-driven war, etc. Suffice to say I'm not optimistic, and I consider death to be very, very bad. It's not at all clear to me that this scenario is worse than status quo, let alone death.
Do we care whether another intelligence is inside or outside of the Hubble volume?
My estimation of the risk from UFAI is lower than (what seems to be) the LW average. I also don't see why limiiting the unfriendlyness of an AI to this MUFAI should be easier than a) an AI which obeys the commands of an individual human on a short time scale and without massive optimization or abstraction or b) an AI which only defends us against X-risks.
I offer this particular scenario because it seems conceivable that with no possible competition between people, it would be possible to avoid doing interpersonal utility comparison, which could make Mostly Friendly AI (MFAI) easier. I don't think this is likely or even worthy of serious consideration, but it might make some of the discussion questions easier to swallow.
1. Value is fragile. But is Eliezer right in thinking that if we get just one piece wrong the whole endeavor is worthless? (Edit: Thanks to Lukeprog for pointing out that this question completely misrepresents EY's position. Error deliberately preserved for educational purposes.)
2. Is the above scenario better or worse than the destruction of all earth-originating intelligence? (This is the same as question 1.)
3. Are there other values (besides affecting-the-real-world) that you would be willing to trade off?
4. Are there other values that, if we traded them off, might make MFAI much easier?
5. If the answers to 3 and 4 overlap, how do we decide which direction to pursue?