For reference, the discussion of this topic took place here:
  
  http://lists.squeakfoundation.org/pipermail/squeak-dev/2021-April/214699.html
  
The motivating concern for Seaside was this:

  https://github.com/SeasideSt/Seaside/issues/1195
  
Dave



On Mon, Apr 12, 2021 at 01:50:57AM +0000, commits at source.squeak.org wrote:
> David T. Lewis uploaded a new version of System to project The Trunk:
> http://source.squeak.org/trunk/System-dtl.1225.mcz
> 
> ==================== Summary ====================
> 
> Name: System-dtl.1225
> Author: dtl
> Time: 11 April 2021, 9:50:52.898233 pm
> UUID: a96e7afc-11cc-48c8-8e72-d63f6295e092
> Ancestors: System-tonyg.1224
> 
> Symbol>>asMutator is used by Seaside, do not deprecate it. Instead let it be a synonym for the preferred Symbol>>asSimpleSetter.
> 
> =============== Diff against System-tonyg.1224 ===============
> 
> Item was added:
> + ----- Method: Symbol>>asMutator (in category '*System-Support') -----
> + asMutator
> + 	"Synonym for asSimpleSetter, retained for support of external packages such as Seaside"
> + 
> + 	^ self asSimpleSetter!
> 
>