ctrl-x-e without executing command immediately

I cannot tell if you will call it simple. This is a quick and dirty proof of concept:

# in Bash

_edit_wo_executing() {
    local editor="${EDITOR:-nano}"
    tmpf="$(mktemp)"
    printf '%s\n' "$READLINE_LINE" > "$tmpf"
    "$editor" "$tmpf"
    READLINE_LINE="$(<"$tmpf")"
    READLINE_POINT="${#READLINE_LINE}"
    rm "$tmpf"
}

bind -x '"\C-x\C-e":_edit_wo_executing'

Now Ctrl xe should do what you want.

Notes:

• I used only basic logic to set editor; adjust it to your needs.

• READLINE_POINT="${#READLINE_LINE}" should place the cursor at the very end. Bash 5 wants the length in characters and the above code works; but Bash 4 wants bytes. To handle non-ASCII text in Bash 4 use

  READLINE_POINT="$(printf '%s' "$READLINE_LINE" | wc -c)"
  

  (I learned from this answer).