If we could fax ourselves to Mars, or undergo uploading, then still wonder whether we're still "us" -- the same as we wonder now when such capabilities are just theoretical/hypotheticals -- that should count as a strong indication that such questions are not very practically relevant, contrary to Aaronson's assertion. Surely we'd need some legal rules, but the basis for those wouldn't be much different than any basis we have now -- we'd still be none the wiser about what identity means, even standing around with our clones.
For example, if we were to wonder about a question of "what effect will a foom-able AI have on our civilization", surely asking after the fact would yield different answers to asking before. With copies / uploads etc., you and your perfect copy could hold a meeting contemplating who stays married with the wife, and still start from the same basis with the same difficulty of finding the "true" answer as if you'd discussed the topic with a pal roleplaying your clone, in the present time.
Scott Aaronson has a new 85 page essay up, titled "The Ghost in the Quantum Turing Machine". (Abstract here.) In Section 2.11 (Singulatarianism) he explicitly mentions Eliezer as an influence. But that's just a starting point, and he then moves in a direction that's very far from any kind of LW consensus. Among other things, he suggests that a crucial qualitative difference between a person and a digital upload is that the laws of physics prohibit making perfect copies of a person. Personally, I find the arguments completely unconvincing, but Aaronson is always thought-provoking and fun to read, and this is a good excuse to read about things like (I quote the abstract) "the No-Cloning Theorem, the measurement problem, decoherence, chaos, the arrow of time, the holographic principle, Newcomb's paradox, Boltzmann brains, algorithmic information theory, and the Common Prior Assumption". This is not just a shopping list of buzzwords, these are all important components of the author's main argument. It unfortunately still seems weak to me, but the time spent reading it is not wasted at all.