I'm trying to figure out what happens when you port this to ARM NEON, and how you catch it with architectures that don't support NEON (they often lack them in Marvell and Allwinner).
CPUs that lack SIMD units can support the functionality (though not the performance of course), and there's even a polyfill library that can lower this API into scalar operations for SIMD-less browsers too.
One thing to keep in mind is that most programmers probably won't want to use this feature directly; it'll be used in libraries that expose higher-level APIs. It's still true that every feature we add increases overall clutter, but SIMD seems sufficently useful and sufficiently self-contained that it's worth the tradeoff.
https://www.dartlang.org/articles/simd/
The primitives are pretty generic, just a few new vector types based on typed arrays. Operations on those types are supported on CPUs without a SIMD unit, they're just slower, but not any slower than coding with non-SIMD operations.
I'm probably nitpicking here, but:
* All Allwinner SoCs have NEON[0]
* Most current ARMv7 processors have NEON. Of the current ARM cores, only Cortex-A5 and Cortex-A9 don't have mandatory NEON support (it's optional). Cortex-A5 is intended for embedded applications. Of the existing Cortex-A9 processors, AFAIK the only somewhat popular one without NEON support is NVIDIA Tegra 2, which is retired. Out of the third party cores, all Qualcomm and Apple ones have NEON support.