Sorry, I guess I got confused about what an L^1 norm meant. My non-confident recollection is that Eliezer believes, not just that we have no idea how to assign measure to worlds, but that our best idea for assigning measure to worlds actively conflicts with the Born rule, except if there exists some sort of mechanism like world-mangling. His endorsement of world-mangling as a possible solution suggests to me that he agrees with its world-counting assumption.