My knowledge of LLVM an SBCL is limited but I know a bit emscripten and how it works. I will look around "multivalues" and "power of two memory access" in LLVM.
Actually getting the support of other language communities would be even more useful. If you can find use-cases of the feature for other languages then it's going to be much more compelling.
A clearer call to action would be helpful here. What exactly should members of the Lisp community who care about this do?