A demonstration of the speed gain you get when using Float32x4 for 3D games can be seen in Web Languages and VMs: Fast Code is Always in Fashion. Now on to the status update:
1. Status of Dart implementation
Dart's implementation of the Float32x4, Uint32x4, and Float32x4List types is complete. The API may change slightly in the future but any changes will be minor and easy to adapt to.
2. Status of Dart acceleration
Dart fully accelerates Float32x4, Uint32x4, and Float32x4List types on IA32, X64, and ARM (with NEON) CPUs. Thanks to Zachary Anderson for the ARM implementation.
3. Status of dart2js support
5. What about AVX and AVX-512?
For those of you who don't follow the latest CPU instruction sets, AVX is the successor to SSE and has 256-bit wide registers (YMM). AVX-512 is a follow up to AVX and adds 512-bit wide registers (ZMM) and doubles (32 instead of 16) the number of register names available. Exciting stuff. AVX exists in the wild and I plan on implementing Float32x8 later this year. AVX-512 was only just announced and no chips support it (yet), once AVX-512 becomes closer to reality Dart will get a Float32x16 type.