ESR's proposal here is basically just another way of spelling Python list comprehensions or Perl 5 map (which is likewise a builtin, with special parsing rules). It's not "new PL territory" by any means.
I think the "new PL territory" was referring to a type-safe generic map builtin. Obviously Python and Perl don't have a concept of type safety. That said, I still wouldn't call that novel in the sense that a builtin version of a well-understood generic function doesn't seem like a feat of ingenuity.
