(require 'cl-seq)                       ; for cl-reduce

(defcustom eww-suggest-uris
  '((lambda ()
      (list (get-text-property (point) 'shr-url)
            (get-text-property (point) 'image-url)))
    'url-get-url-at-point
    (lambda ()
      (plist-get eww-data :url)))
  "List of functions called to form the list of default URIs for `eww'.
Each of the elements is a function returning either a string or a list
of strings.  The results will be joined into a single list with
duplicate entries (if any) removed."
  :version "25.1"
  :group 'eww
  :type 'hook)

(defun eww-suggested-uris nil
  "Return the list of URIs to suggest at the `eww' prompt.
This list can be customized via `eww-suggest-uris'."
  (let ((obseen (make-vector 42 0)))
    (cl-reduce (lambda (acc elt)
                 (let ((uri (funcall elt)))
                   (if (or (not acc) (intern-soft uri obseen))
                       acc
                     (intern uri obseen)
                     (cons uri acc))))
               eww-suggest-uris
               :initial-value nil)))