I want to be able to set a keyword filter, to display only certain events of a Team Calendar on a Confluence page. But it is not feasible to create multiple Calendars because it will be a maintenance nightmare.
Perhaps when you add the gadget, one of the fields can let you filter by keyword.
Another option would be to consider introducing "Event" types and allowing users to make their own events and filter by the event types. This overlaps with TEAMCAL-523 quite a bit.