Agreed. For instance, the piped bc sed thing's error handling is apparently brok...

Agreed. For instance, the piped bc sed thing's error handling is apparently broken, and no one has pointed that out yet. pipefail and $() don't play nice with each other:

   #!/bin/bash
   set -euo pipefail
   echo $(false|true)
   echo a
   echo $(false)
   echo b
   false
   echo c

Prints 'ab'.