We forgot to mention one addition to the API in the update for revision Beta 58 on 6th May 2013:
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API - Added: The API Search interface can now sort Unread Submissions in reverse date order (oldest first). Use value "unread_datetime_reverse" for property "orderby".
And of course, sorting Unread Submissions by oldest first in the web interface was a feature we did remember to announce in that version. :P