These few functions may help Asciidoctor editors to enable live preview in Emacs Editor.

These functions have been isolated from my package RCD Utilities.

(defun rcd-command-output-from-input (program input &rest args)
  "Returns output from PROGRAM INPUT with optional ARGS"
  (let* ((output (with-temp-buffer
		   (insert input)
		   (apply #'call-process-region nil nil program t t nil args)

(defun rcd-asciidoctor (string &rest args)
  "Returns plain text from Markdown by using pandoc"
  (apply 'rcd-command-output-from-input "asciidoctor" string "-" args))

(defun rcd-asciidoctor-preview ()
  "Preview asciidoctor"
  (let* ((output (rcd-asciidoctor (buffer-string)))
	 (file (concat (or (getenv "TMPDIR") "/tmp/") "asciidoctor.html")))
    (with-temp-file file (insert output))
    (browse-url file)))
I recommend setting it up on a user key such as C-c a:
(global-set-key (kbd "C-c a") 'rcd-asciidoctor-preview)

See the preview on video