WebAssembly doesn't make native integration any easier than JS. Neither defines the exact way so called non-web embeddings actually are defined and both can support it. I honestly have no idea the relevance of WebAssembly in this discussion. Could you provide an illustrative example?
Edit: I should clarify that for certain types of apps WebAssembly might be relevant but the discussion seemed to be out UI layer and I don't understand how WebAssembly fills a gap that a native API in JS could also provide along with the same challenges.
I'm sorry, I'm using "native" in an unclear way (that should have been obvious to me). I don't mean it will help with native API integration (JavaScript can do that just fine), I mean as a replacement for machine code on both platforms. iOS of course uses machine code for everything, but on Android it's mostly whittled down to the minimum: things that Java can't do efficiently, or code that isn't Java. That's the role I hope WebAssembly can fill, but it still remains to be seen how usable their solutions for threads, SIMD, etc. are.
A good example is games. Some do manage to use Java, but it's mostly a hindrance; being able to compile languages with a C style ontology to a platform-independent and efficient VM would be very helpful here.
Edit: I should clarify that for certain types of apps WebAssembly might be relevant but the discussion seemed to be out UI layer and I don't understand how WebAssembly fills a gap that a native API in JS could also provide along with the same challenges.