Is AliasAssign Now Official?

[surlymoor]

While reading through the spec to resolve some impressive idiocy 
of mine, I noticed that [alias mutability (given some 
constraints) is officially part of 
D](https://dlang.org/spec/declaration.html#AliasAssign). 
Previously, I knew this to be an experimental feature, and its 
seemingly most salient benefit is that of a more readable 
alternative to recursive templates. This is nice, but shouldn't a 
DIP have been required for its inclusion outside of the preview 
switch? Might I and others use it knowing that it won't be 
rescinded in future versions of the frontend?