But we should, for example, consider the projected enjoyment of people we imagine visiting our nature preserves 500 years from now, as if their enjoyment were as important as our own, not discounting at all for the risk that they may not even exist.

Eliezer doesn't disagree: as he says more than once, he's talking about pure preferences, intrinsic values. Other risks do need to be incorporated, but it seems better to do so directly, rather than through a discounting heuristic. Larks seems to implicitly be doing this with his P(AGI) = 10^-9.