AFAIK PEP 638 is not being worked on, but if you’d like to start macros right now, there are existing libraries which are (in my opinion) better-implemented.
There’s the venerable MacroPy3 library (abandoned many years ago, but still works flawlessly!)
Then there’s the now-abandoned rewrite mcpy, inspired by MacroPy
and there’s the modern (still maintained i think) mcpyrate, originally forked from mcpy but has since diverged and been fleshed out with extra features