wasm spec is fully defined and public, and we even already have source for browsers.

What prevents developing a wrapper or shim that runs any wasm as if it were any other native executable?

You might be legally prevented from redistributing the wasm, so maybe you can't bundle it right into a .deb or.rpm, but it's trivial in that case to just download on the fly if not exist and re-use after that. You may want it to check for updates all the time anyway.