In the accepted version of SE-0525, conformances of concrete SIMD types to ConvertibleToBytes and ConvertibleFromBytes were listed as a future direction. These have now been rolled into the implementation of the main feature (with the exception that SIMD3 does not conform to ConvertibleToBytes due to its tail padding).
The language steering group has decided to update the proposal text to reflect these additions as a bugfix. We don't anticipate that there are plausible alternatives in the design space here that would benefit from review, but please feel free to use this thread to discuss if you have thoughts or comments.
Xiaodi Wu
Review Manager