Among other problems, each worker has to instantiate all the host javascript objects and instantiate its own copy of the wasm module, which has its own unique c

Among other problems, each worker has to instantiate all the host javascript objects and instantiate its own copy of the wasm module, which has its own unique copy of the imports and the function pointer table. It's definitely way less elegant than real threads and potentially creates performance and stability issues. You also now have fun thread affinity problems, like if you call setTimeout your timer IDs now have thread affinity, which is nonsense.