There's no reason to think it won't help - the encoder/decoder code base could be written in WASM directly to ensure it uses the SIMD instructions, and those will hopefully map closely to the machine SIMD instructions.

Of course though, you're right that it'll still incur a performance penalty.

Someone needs to make a dev environment where someone can write WASM and see realtime the generated assembly instructions, together with the number of cycles to execute.

That way, the developer can tweak the input to the compiler to get exactly the sequence of instructions they wanted.

They can also hand write the output assembly, and put a patch in to the compiler saying "this generated assembly is faster that what you generated, so please generate this in the next version".