What are the plans for thread-local and shared global variables?

AFAICT for the current web embedding of WebAssembly, globals are effectively thread-local: you have to create a new instance of a module for each JavaScript worker, so any mutable globals will also be duplicated for each worker. Is that correct?

I assume that's not as efficient as allowing instances to be shared between workers, and adding some form of thread-local variables.

Do we need shared global variables? Shared vs thread-local is only meaningful for mutable variables, and mutable shared globals can be lowered to an immutable global address into shared memory, so it might be simpler to just omit shared globals.

The issue contains no file, test, or entry point to inspect, and asks unresolved design questions about thread-local and shared global variables. First establish the intended WebAssembly threading model and an agreed scope; no concrete done condition is stated beyond resolving those questions.