The question is,
is WASM's security model / sandbox "safer" / "easier to actually execute" than JS'?
Of course JS ain't gonna go anywhere now, but if popular JS frameworks started emitting WebAssembly behind the scenes, so devs could still write their JS(and C++/C#/etc) code, but it'd use WASM under the hood then that'd start process of the deprecation of JS.
Which would mean that after all popular JS frameworks managed to migrate and popular sites adopted to this, then in ideal world you'd be able to turn off javascript and still use those sites/apps via WASM, not by default for everyone, but at least users that care would have an option to do so while still being able to use the web.
You gotta start somewhere
I'm wrong somewhere? or out of the touch with reality?
https://developer.mozilla.org/en-US/docs/WebAssembly
As for vulnerabilities, here are nccgroup's slides about WASM explots:
https://i.blackhat.com/us-18/Thu-August-9/us-18-Lukasiewicz-...
Here's an example vulnerability in WASM parsing leading to RCE:
https://labs.f-secure.com/assets/BlogFiles/apple-safari-wasm...
What could happen is that browsers will support wasm natively and they'll translate JS into wasm. I'm not qualified enough to judge whether it would be possible to achieve current levels of JS performance with that approach, but theoretically it could be possible. In this case only wasm security will matter.
But I did not hear about any kinds of those plans, those are just my wild speculations. So deprecating of JS is not going to happen anytime soon. Wasm will accompany JS and that's about it for the foreseeable future.
Your question is non-sensical as is. I think you need to expand it to have people be less confused as to what you’re asking.