Eh, I'm not trying to discourage you from building cool apps on top of WASI. I just hope you understand what you're up against. And most of it is not technical; you've got to convince Apple to include a WASI runtime on iOS (among others).

Just like any new feature added to the web standard requires that Apple actually implement it in Safari, right?

I'm not really pro-WASI so much as I am against the idea that the browser is a good application platform.

Right, just like that. They are totally comparable, adding a new feature to an existing runtime is just as hard to convince as adding a new runtime itself. Totally comparable.

My understanding is that Apple still doesn't implement some new web standards, so yeah actually.

Ultimately, if a vendor refuses to support something, it doesn't matter if it is an 'open standard' or not. The openness means absolutely nothing in this instance.