How bad would it be to be conservative with a macro `simdex` ("simd index" ;P ) like

```rust
simdex![v, 0, 0, 1, 1, 2, 2, 3, 3];

simdex![v, xyz];
// (or maybe)
simdex![v, x, y, z];
```
which doesn't require magical "field access" overloading.