In the process I also added the possibility to remove Announcements from an AnnouncementSet and I would like to push this in Pharo 6.0. One thing I would work on is to add to Annoucements the possibility of filtering announcements based on instances not just types. This is a longer term plan.
Filtering on instances is in the same category of making actual delivery after subscription more dynamic; both also have the effect that it becomes even harder to reason about what is going to happen as a result of an Announcement without actually running the code.
IMHO, if the logic is "I want to handle this announcement some of the time", that is much easier to understand if handled explicitly in announcement handling code, rather than through state changes to the announcement delivery.
As I think Glamour is a poster child for, current usage patterns can already be hard to follow ;)
Cheers,
Henry