The following code allows you to sort tasks based on regexp matches
against the line. It’s fairly simple, but may give people ideas about
fancier task sorting.

(setq planner-sort-tasks-key-function 'planner-sort-tasks-by-score)

(defvar planner-score-rules '(("read" . 50))
  "Alist of planner scoring rules of the form (regexp . score-value).
Tasks with higher scores are listed first.")

(defun planner-sort-tasks-by-score ()
  "Sort tasks by the rule in the table."
  (let ((score 0)
        (case-fold-search t)
        (line (buffer-substring-no-properties (line-beginning-position)
                                              (line-end-position))))
    (mapc
     (lambda (item)
       (when (string-match (car item) line)
         (setq score (- score (cdr item)))))
     planner-score-rules)
    score))