* the page is automatically published on some date (i.e. build, linked, syndicated, inlined/mapped, etc.)
* the page is automatically unpublished at some other date (i.e. removed)
I know that ikiwiki is a wiki compiler so that something has to refresh the wiki periodically to enforce the rules (a cronjob for instance). It seems to me that the calendar plugin rely on something similar.
The date for publishing and expiring could be set be using some new directives; an alternative could be to expand the [[plugin/meta]] plugin with [<span/>[!meta date="auto publish date"]] and [<span/>[!meta expires="auto expire date"]].