I don't think inclusion in 3.9 should be automatic.  

The purpose of the deferment is to evaluate the premise, "the only reason people have found this notation confusing was that it wasn't yet valid syntax available for use in their own code."  If that premise turns out to be false, we should think seriously about whether this makes the docs less approachable for everyday users.

This extensive edit of the docs will change the appearance and texture of language from day 1 of a person's exposure to the language.  It warrants careful consideration of the costs and benefits.  Despite what we might wish to be true, the cost side of the equation is definitely not zero.