I have a dollar that says all platform difference issues will be solved by just doing whatever POSIX does and expecting the host OS to figure it out if it isn't already POSIX. Whenever you try to abstract away arbitrarily different implementations while retaining their non-common functionality you either end up reimplementing one of them and expecting the others to work around it, or you end up forcing the programmer to bypass the abstraction anyway and implement logic for each implementation.

I wouldn't count on that.

I have worked on file APIs. There are so many differences between Windows and Posix that abstracting them away just doesn't work. Undoubtedly, there will eventually be platform-specific APIs that implement one or the other, and cross-platform APIs that implement the intersection.

It's a good question. WASI currently doesn't allow you to set custom access-control permissions when creating files. But we're just getting started, so if we can find a design that works, we can add it.