> Asm.js seems like an interesting project but one of the issues that (I like to think) the VM approach would solve is that the semantics could be more low-level.

Can you elaborate? asm.js semantics are already low-level, in fact as I said in another comment, they are lower than some VMs (e.g. PNaCl).

Which part of asm.js do you find to be too high-level?