I just noticed that spacemacs installed an old version of org-drill.
org-drill is out-of-date on elpa. From my ~/.emacs.d/elpa/org-plus-contrib-20170717/org-drill.el :
;;; Version: 2.4.7
Emacs-devel wouldn't be the right place for this query.
I have copied the package author on this thread. They need to update the package on Org contrib/ themselves (A better scenario would be if the author is willing to assign their copyright to FSF. In that case, the package can even land in the official Org repo, not just contrib/).
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