The SIRI document Part 3 stated that "Passengers do not expect vehicles that have already arrived at the stop to continue to be shown on a display. The MonitoredStopVisitCancellation element is used to cleardown an earlier MonitoredStopVisit..."
It means that originally it was meant for clear down but I agree it could be used for more than that.
How long will you keep submitting the cancellation message ?
Will it be one time message or message sent for a period of time in case some client did not receive it (in case many clients are registrated to the same gateway SIRI server like in the case we have here in Israel)
The last Edition of the document was on 2007 but there is a draft new version from 2012.