Came also across this PR the other day. Certainly a feature I would love to see. More so since the base R pipe which has been added in R 4.1 will supposedly support an underscore operator with the same functionality in R 4.2 (would be neat to have roughly the same base piping functionalities in both languages without extra packages).
I was looking for it, but couldn’t find it (but I also have heard, and not read about it iirc). I spent some more time checking and so far no changes to the pipe implementation have been made in 4.2 dev if I can tell correctly (usually I am not that deep into language internals). r-svn/gram.c at master · r-devel/r-svn · GitHub
It’s hard to work on it without getting clear buy-in from the core devs on the semantics.
Personally, I favor the Scala-like “tight-binding” semantics of the original PR, which is backwards-compatible, simple to explain and reason about, and gives clear improvements in simple cases (while for everything else you can use ->).
Every attempt to devise a more expansive DWIM syntax (to handle compound expressions like 1 + 2_) led to confusion, breakage, and ultimately ground progress to a halt.