> George Mauer writes:
>> is there a straightforward way to extend the org parser to do this?
> I don't think so. It seems the emphasis markers are hard-coded
> in various places.
>
> From a quick look at the code, you'd have to customize
> `org-emphasis-alist` and redefine `org-set-emph-re`  and
> `org-do-emphasis-faces`. Maybe that'd be enough.
>

I did just what you said, and I've inserted what's bellow, somewhere in my `init.org` / 
`init.el`, before anything `org-mode` related (save for two `hook`):
(Note it is an almost exact copy from `org.el`, I've only changed a few characters. And 
added the `advice-add override`.)

#+begin_src emacs-lisp
  (defun org-set-emph-re-fixed (var val)
    "Set variable and compute the emphasis regular expression."
    (set var val)
    (when (and (boundp 'org-emphasis-alist)
               (boundp 'org-emphasis-regexp-components)
               org-emphasis-alist org-emphasis-regexp-components)
      (pcase-let*
          ((`(,pre ,post ,border ,body ,nl) org-emphasis-regexp-components)
           (body (if (<= nl 0) body
                   (format "%s*?\\(?:\n%s*?\\)\\{0,%d\\}" body body nl)))
           (template
            (format (concat "\\([%s]\\|^\\)" ;before markers
                            "\\(\\([%%s]\\)\\([^%s]\\|[^%s]%s[^%s]\\)\\3\\)"
                            "\\([%s]\\|$\\)") ;after markers
                    pre border border body border post)))
        (setq org-emph-re (format template "*/_+"))
        (setq org-verbatim-re (format template "=~`")))))

  (advice-add 'org-set-emph-re :override #'org-set-emph-re-fixed)
#+end_src

#+begin_src emacs-lisp
  (defun org-do-emphasis-faces-fixed (limit)
    "Run through the buffer and emphasize strings."
    (let ((quick-re (format "\\([%s]\\|^\\)\\([~`=*/_+]\\)"
                            (car org-emphasis-regexp-components))))
      (catch :exit
        (while (re-search-forward quick-re limit t)
          (let* ((marker (match-string 2))
                 (verbatim? (member marker '("~" "`" "="))))
            (when (save-excursion
                    (goto-char (match-beginning 0))
                    (and
                     ;; Do not match table hlines.
                     (not (and (equal marker "+")
                               (org-match-line
                                "[ \t]*\\(|[-+]+|?\\|\\+[-+]+\\+\\)[ \t]*$")))
                     ;; Do not match headline stars.  Do not consider
                     ;; stars of a headline as closing marker for bold
                     ;; markup either.
                     (not (and (equal marker "*")
                               (save-excursion
                                 (forward-char)
                                 (skip-chars-backward "*")
                                 (looking-at-p org-outline-regexp-bol))))
                     ;; Match full emphasis markup regexp.
                     (looking-at (if verbatim? org-verbatim-re org-emph-re))
                     ;; Do not span over paragraph boundaries.
                     (not (string-match-p org-element-paragraph-separate
                                          (match-string 2)))
                     ;; Do not span over cells in table rows.
                     (not (and (save-match-data (org-match-line "[ \t]*|"))
                               (string-match-p "|" (match-string 4))))))
              (pcase-let ((`(,_ ,face ,_) (assoc marker org-emphasis-alist))
                          (m (if org-hide-emphasis-markers 4 2)))
                (font-lock-prepend-text-property
                 (match-beginning m) (match-end m) 'face face)
                (when verbatim?
                  (org-remove-flyspell-overlays-in
                   (match-beginning 0) (match-end 0))
                  (remove-text-properties (match-beginning 2) (match-end 2)
                                          '(display t invisible t intangible t)))
                (add-text-properties (match-beginning 2) (match-end 2)
                                     '(font-lock-multiline t org-emphasis t))
                (when (and org-hide-emphasis-markers
                           (not (org-at-comment-p)))
                  (add-text-properties (match-end 4) (match-beginning 5)
                                       '(invisible t))
                  (add-text-properties (match-beginning 3) (match-end 3)
                                       '(invisible t)))
                (throw :exit t))))))))