I believe that in many ways, this would be ideal. Not only could any language be used (the implementers being responsible for interfacing with the browser API),

I believe that in many ways, this would be ideal. Not only could any language be used (the implementers being responsible for interfacing with the browser API), but the LLVM pseudo-asm could be pre-optimized saving the browser a lot of work. In the meantime, browsers would still be free to compete based on their JIT implementations. With rust and by proxy, Mozilla/Samsung's experimental Servo layout engine targeting the LLVM, I can also see potential synergy in this situation.