How can you get Org Mode to create and schedule entries within a year-month-day outline structure? You can define an org-capture-templates with the keyword file+datetree+prompt. This lets you specify a date for your entry, and Org will create the entry in a hierarchy organized by year, month, and day.

If you’d like to display the entry in your agenda, you’ll also need an active timestamp of the form <yyyy-mm-dd>. Fortunately, you can reuse the date you specified at the initial prompt to create the datetree entry. Looking at org-capture.el will show you that the org-capture function refers to the org-read-date-final-answer, which is set to whatever string you entered at the date prompt. For example, if you entered 18, then org-read-date-final-answer will be set to 18. You can use org-read-date to convert this back to a yyyy-mm-dd-style date.

How do you use this in org-capture-templates? You can use the %(...) syntax for calling an Emacs Lisp expression, like so:

(setq org-capture-templates '(
  ;; other entries go here
  ("s" "Journal entry with date, scheduled" entry
   (file+datetree+prompt "~/personal/journal.org")
    "* %^{Title}\n<%(org-read-date nil nil org-read-date-final-answer)>\n%i\n%?\n")))

Here’s sample output from that capture template:

* 2015
** 2015-12 December
*** 2015-12-31 Thursday
**** End of the year party!
<2015-12-31>

Thanks to Sean Miller for the nudge to think about this!