Did I miss something? If I am right, I offer to write the necessary patch, copied and adapted from the tag plugin, to generate the pages `archive_base/year/month.mdwn` on the fly.
--- Spalax
+-- [[Louis|spalax]]
> Good spotting, `ikiwiki-calendar` predates the `add_autofile` API used to
> autocreate tag pages and was bolted in as an easy way to create calendar
> That last is, arguably, the real point of running ikiwiki-calendar in
> a cron job. Of course all it really does is run `ikiwiki -setup foo
> -refresh`. --[[Joey]]
+
+> > [[Patch|todo/calendar_autocreate]]. -- [[Louis|spalax]]