Julien Danjou <julien@danjou.info> writes:
> Hi there,
>
> As promised yesterday, here's my patch!
>
> It adds `gnus-completion-styles' which set `completion-styles' when calling
> `completing-read'.

I like your idea, and your patch. Thank you.

> It adds `gnus-use-ido' which makes `gnus-completing-read' use
> `ido-completing-read' rather than `completing-read'

I don't like that too much. How about something along the lines of

--8<---------------cut here---------------start------------->8---
(defun pod-completing-read (prompt choices)
  "Use `completing-read' to do a completing read."
  (completing-read prompt choices))

(defun pod-icompleting-read (prompt choices)
  "Use iswitchb to do a completing read."
  (let ((iswitchb-make-buflist-hook
         (lambda ()
           (setq iswitchb-temp-buflist choices))))
    (unwind-protect
        (progn
          (when (not iswitchb-mode)
            (add-hook 'minibuffer-setup-hook 'iswitchb-minibuffer-setup))
          (iswitchb-read-buffer prompt))
      (when (not iswitchb-mode)
        (remove-hook 'minibuffer-setup-hook 'iswitchb-minibuffer-setup)))))

(defun pod-ido-completing-read (prompt choices)
  "Use ido to do a completing read."
  (ido-completing-read prompt choices))

(defcustom pod-completing-read-function
  #'pod-icompleting-read
  "Ask the user to select a single item from a list.
Used by `pod-link-section', `pod-link-module', and
`pod-link-module-section'."
  :group 'pod-mode
  :type '(radio (function-item
                 :doc "Use Emacs' standard `completing-read' function."
                 pod-completing-read)
                (function-item :doc "Use iswitchb's completing-read function."
                               pod-icompleting-read)
                (function-item :doc "Use ido's completing-read function."
                               pod-ido-completing-read)
                (function)))

(defun pod-do-completing-read (&rest args)
  "Do a completing read with the configured `pod-completing-read-function'."
  (apply pod-completing-read-function args))
--8<---------------cut here---------------end--------------->8---

This is what I did a couple of months back for pod-mode.el. I believe it
makes for nicer customisation. If you like this as well, I'd be happy to
prepare an updated patch using the above, and extending it also support
REQUIRE-MATCH, INITIAL-INPUT, HISTORY, etc.