I don't think those are happening, but how about basic set arithmetic? The fact that you can't do difference / union / intersection using the standard library is frustrating.
There's a proposal for that.
Two of them now. One to add Set-specific methods, and another to port the usual Array.prototype methods over to Set and Maps. Can't wait!
Unlikely. Mozilla had extensions which they submitted for ES6 IIRC (lists and generators) but it seems the tc39 preferred going with HoFs instead.
Thanks. On the face of it it seems a bit of a shame to me. My experience writing python daily (since before dict and set comprehensions were introduced) is that the comprehension syntax is used extremely commonly in a large codebase and that the way that you can specify both the transformation and the filtering in a single comprehension is much more readable than composing a map and a filter.