You’ll need to explain that to those of us who use Emacs for professional work. What fails for you? In particular, what fails that needs threading to be resolved?

Networking activity is a prime example of something where threading is least likely to be a clearly superior solution. Heavy CPU use is where threading may be the superior choice and a single event-loop thread is not. IO waiting is not.

Emacs can run subprocesses just fine. I assumed you wanted a solution to a problem rather than an exercise.

With filenames:

for file in `find . -name "*.org"`; do sed -nr "s;.*notmuch:id:([^]\n]*).*$;$file: \1;p" "$file"; done

find . -name "*.org" -exec sed -nr 's/.*notmuch:id:([^]\n]*).*$/\1/p' {} \;