I hope you're right. But how is WASM going to answer questions like "how does the application play sound?" or "how does the application request a password from the system keychain?"

WASM solves a lot of problems, but I don't think its chances of providing a uniform API to things like that are any better than Snap/Flatpak's, because those problems are fundamentally not about the runtime/packaging system. They're caused by OS functionality being a fragmented and moving target. Directly executable applications have to deal with those complexities themselves. Containerized applications in WASM/Docker/Snap/Flatpak/whatever rely on the container layer to do it. But someone's software has to chase that moving target, and it moves very fast.