The current draft is available at http://tc39.github.io/ecmascript_sharedmem/shmem.html

The two strengths provided by the model are sequentially consistent atomics and something between the strengths of C++'s non-atomics and relaxed atomics. Races are fully defined, and there is no undefined behavior or undefined values.

I'm happy to discuss things more in a new thread or in private communication and would prefer to not derail this thread about VLC.