Wasm has a pretty simple execution model, wouldn’t be hard to write something that preprocesses wasm code during load, similar to what you can do with java classloaders.
Declaring something obsolete doesn't make it so. Flash went away because of iPhone and rise of mobile app and still it took about a decade for it to be irrelevant. Without a similar tectonic shift, it would take longer.
I don't think WASM can write to its code memory to self-decrypt. At some point, the WASM has to create a DOM node containing the decrypted script, at which point you can process the code.
