To the extent that asm.js and JavaScript are, yes. Everything is well-defined, so in theory any Turing machine should be able to run it, but it's certainly going to be easier to implement efficiently on a typical modern 32-bit or 64-bit CPU in a computer or phone than on something more unusual.
Yep! It's a completely portable target and fulfils the promise of “compile once, run anywhere”, although how well it runs depends on the particular browser.
(It is pretty amazing you can compile C code to something that actually runs on multiple machines, it's very nice.)
That is a good question. I imagine it depends on why it is a native module. If they are native module because it utilizing features at the OS or machine level, then I doubt they could.
That's not really true. With JS glue code (including many libraries already written) Wasm modules can access anything JS can do. E.g. there are Wasm demos showing access to WebGL2, audio generation, camera/microphone, HTTP, storage, gamepads, ...
That's the point. a WASM app has access to the same Web APIs that JS does, for the most part. This was in response to the claim that WASM only gets to work off of a limited api, not an argument as to why WASM is an improvement over JS.
Which is to say that they assume little-endian just like asm.js and modern JavaScript do. Architectures other than ARM and x86 are mostly dead so this isn't generally a huge problem except for the handful of die-hard Amiga users.
