Who's optimizing for a specific version of V8? Avoiding inherently slow
things (such as for-in loops over slow objects, or needless polymorphism,
etc) in your JS code makes a lot of sense regardless of the VM you're
Sure, some deopts may no longer happen in an upcoming version, but then
again maybe they still will, and maybe you want better performance *now*
rather than possibly at some unspecified date in the future.