I'd like to see a new feature using mapmaker maps as the filter for alerts or reports.
Basically if any node or interface on a map is down - send me an alert.
Also using the map as a Report Writer filter - show me the latency for all nodes on a map, or bandwidth utilization for all interfaces on a map.
Simply adding or removing nodes and or interfaces from a map will dynamically update your alerting or reporting based on that map.
No need to mess with custom properties :-p