[sunfish]

For historical reasons, every language that wanted one built their own SIMD API instead of building a language-independent API first: C++, C#, Dart, OpenCL, and so on, and it's not easy to go back and change that. However, there is a lot of commonality between the SIMD APIs in those languages, so we are following de-facto standards here.

And, we certainly do have real-world use cases in mind. See [0] for one example. We're also interested in using SIMD for video codec development which can't always be done on GPUs.

[0] http://blogs.unity3d.com/2014/10/07/benchmarking-unity-perfo...

And if, in the future, Apple can show that auto-vectorization in this domain is more successful than their attempts so far have shown it to be, then JS engines can always just go back to implementing SIMD.js via a simple polyfill which the engine can auto-vectorize, leaving very little baggage in the language or implementations.