And Figma could be a 20B buyout without WASM. I don't see any relevancy about valuation and a specific tech choice. Figma's editor is a very good use case for WASM -especially since they have the right people in the team- but there are other ways to achieve the same thing (even just by using JS).
I don't think the economics of write-once-run-anywhere are going to change anytime soon. so WASM is a welcome shift closer to the metal, I'd say.
From a security/privacy perspective electron-esque apps are no different from native apps, and divorced from the browser UX, PWAs only inherit the trust they cultivated while running in the browser. They are just webapps with some quality-of-life sprinkled on top, after all.
With WASM, it is like machine code for the browser meant to obscure what is even happening and you are supposed to just trust it and I don't. I don't trust it to not be abused to push more privacy violations and I don't trust most web developers enough to not just pull in a huge framework with no clue what they are doing and to make accessible fast sites using it.
Native apps are objectively worse than WASM in terms of security/privacy risks as they have access to all userspace syscalls. It's not like WASM bytecode can link against system libraries. Everything has to go through the browser/runtime sandbox. The only real risk here is side-channel attacks like Meltdown.
No, not at all. It means users can run whatever software they want on their machine.