Had the following idea:
What if there was an event interface that could be implemented by various services, whose job was to "report status"; things like pool sizes, loaded pages, components, etc.
Lets call the event interface MonitorListener
public void monitorStatusRequested(MonitorEvent event);
Service implementations could register with the service (say tapestry.monitor.MonitorEventCoordinator).
A page or component could uses the coordinator service to query the services of Tapestry and format it into an HTML report. Leverage the DescriptionReceiver interface (the event could implement the interface, or provide a receiver object that does). The "Engine" tab of the Inspector could make use of this as well.
This would be a great way to gain some introspection into the underlying status of Tapestry without cluttering up all the service interfaces.