Oh, and I forgot one more thing:
As I read the internals, I noticed many times that PHP lexer is
somewhat limited in it's capabilities and sometimes the features are
dropped because of this issue.
It can be the case that the can be ambiguous and it will be just
impossible to add at this stage.
As Ryan McCue pointed out in his example - there can be a problem with
arrays. And so on. Use cases are not just limited to declaring a
lambda as a function callback or assigning it to a variable. Creatinx
syntax that just looks odd for the language like those | probably will
not be accepted by the community because it looks out of place.
my 2 cents