Good summary of what I thought Greg FitzPatrick/SKICal were looking for in an "unscheduled event" also.
There are some more requirements that need to be worked out on this. Maybe Greg and SKICal team can comment/provide contributions. For example, what properties are needed for these kinds of "events"? Are these something that would appear on a "Planner" view of the calendar store or the "Calendar" view? If the latter, then we probably want to look at modifying the RFC2426 restriction tables for VEVENT, rather than a new component. Can we get by with keeping these as VEVENTs that have a DTSTART/DTEND, but a special priority and category for these "unscheduled events".
-- Frank